The Natural History of Ireland/Volume 4/Mus Hibernicus, Thompson

by William Thompson

Mus Hibernicus, Thompson.

I made the following communication, on this species, to the Zoological Society of London, in 1837, in the proceedings for which year it was published : — "Mus Hibernicus (lrish. Rat).On questioning a person, some years ago, respecting a black rat which he had seen in the North of Ireland, my curiosity was excited by the statement that it had a white breast. In autumn last, a similar description was given me of one that had been caught, some time before, in Tollymore Park (County of Down). Mr. R. Ball, of Dublin, informs me that black rats, with the breast white, have been reported to him as once common about Youghal (County of Cork), though they are now very rare or perhaps extinct. But until April last, when a specimen was sent from Rathfriland (County of Down) to the Belfast Museum, I had not an opportunity either of seeing or examming the animal. This individual differs from the M. rattus, as described by authors, and also from specimens preserved in the British Museum, and in the collection of this society, in the relative proportion of the tail to that of the head and body ; in having shorter ears, and in their being better clothed with hair, as is the tail likewise ; and in the fur of the body being of a softer texture. The difference in colour between the M. rattus and the present specimen is, that the latter exhibits a somewhat triangular spot of pure white extending about nine lines below the breast, and has the fore-feet of the same colour. " The following is a comparison of this specimen with the M. rattus, as given by Mr. Jenyns. The same dimensions, with the very trivial difference of the ears being half a line less, appear in Mr. Bell's British Quadrupeds.

• Length of the head and body M. Hibernicus 7 inches 6 lines M. Rattus 7 inches 4 lines
• Length of the head M. Hibernicus 1 inch 10 lines M. Rattus 1 inch 10 lines
• Length of the ears M. Hibernicus 0 inches 9 lines M. Rattus 0 inches 11 and 1/2 lines
• Length of the tail M. Hibernicus 5 inches 6 lines M. Rattus 7 inches 11 lines
• Length from the base of the ear to the snout M. Hibernicus 1 inch 6 lines
• Length from from the tarsal joint to the end of the toes M. Hibernicus 1 inch 6 lines

These differences incline me to consider this animal distinct from M. rattus and, being unable to find any species described with which it accords, I propose to name it provisionally M. Hibernicus. Should future investigation prove it to be a variety only of M. rattus, it can be so considered under the present appellation."

The following information has been since obtained:-In March, 1838, Robert Langtry, Esq., informed me that, about fifteen or sixteen years previously, eighteen of these animals were killed, along with a great many common rats, during the " taking-in of a stack" of grain, at Fort William, near Belfast. There were three generations- of them, viz.- two adults, several well grown, but apparently not mature, and a number of young ones.They were nearly all killed by himself, and neither before nor since were any seen about the place. He described the animals so accurately,as to white breast, &c., that there is not a shadow of doubt relative to his correctness. The presence of three generations of this animal, in the same stack, with a great number of the Mus decumanus, speaks I think decisively against the latter species destroying them.Mr. Edward Benn, who has frequently heard of the capture of black rats with white spots on their breasts, had it always described to him as being shorter in the tail than a second species of black rat, also described to him, and which was, perhaps, Mus rattus, a specimen of which, as already mentioned, he procured for me, in December, 1842. This gentleman had learned that black rats with white spots on the breast were, at one time, not uncommon about a flour-mill at Carrickfergus. In August, 1843, I questioned the gamekeeper at Tollymore Park on the subject of this species, and he stated that he got a black rat there, about fourteen years before that date. It had a white breast ; its tail, he was certain, was shorter than that of the common rat; and he felt sure that it could not have been a variety of the common species, for various reasons which he explained. Were there not a difference in form, I should bring this animal under Mus rattus, as a variety ; but, as those who have seen it all describe it to have a shorter tail than that species, I still retain it under the above provisional name. What is stated of this animal leads me to consider it asat least a permanent variety of Mus rattus.

Note.The following memoranda were made by Mr. Thompson, after the foregoing remarks had been written. The two specimens referredto in these memoranda are now in the Belfast Museum.Ed.

" March 1st, 1850. Mus rattus?- M. Hibernicus- A very large rat of this species (large even for M. decumanus) was brought me to look at to-day, in the flesh. It was killed at Cogry Mills, near Doagh (County Antrim). Its weight is 1 lb. 3 oz. ; it is a male. It is wholly black, except a white elongate marking, an inch and half long, upon the breast, and a little white on the toes.

• Length from snout to base of tail 11 inches 0 lines
• Length of tail, which is imperfect 8 inches 3 lines
• Length of head 2 inches 8 lines
• Length of ears 10 and 1/2 lines

"March 1st, 1851.- Black Rat, with white spot on breast.- A very fine one was sent me by Mr. Wm. Marshall, of Barn Cottage (near Carrickfergus) ; its weight, 13 and 1/4 oz. avoirdupois."