NOTES ON THE CAMBRIDGE GREENSAND. 491
There is another form, however, with which they have some relations, viz. A. sexangulcitus, Seeley. To the figured type of this they have little resemblance ; but other specimens which Mr. Seeley has recently referred to this species are very like them, and, if he is not mistaken in these later determinations, I think the above name must also be added to the synonymy of A. rliamno- notus. It is possible that the two originally described specimens may really be a distinct species ; but I am more inclined to consider that these constitute a strongly marked variety of this variable form, for which the varietal designation sexangulatus may be conveniently retained.
In thus proposing to group under one specific name several forms which, in their extreme modifications, are very unlike one another, I am ouly following the plan suggested by Mr. Seeley himself in his excellent paper on the Cambridge Ammonites, in which he describes numerous varieties of the four types, splendens, auritus, Raulinianus, and Studeri, regarding these as but subspecies of a larger group, for which he suggests the name of A. permutatus.
Ammonites ccelonotus, Seeley.
A. coelonotus, var., Seelev, Ann. & Mag. Nat. Hist. 3rd ser. vol. xvi. p. 238, pi. x. fig. 3.
A. valbonnensis, Hebert & Mun.-Ch. in Description du Bassin d'Uchaux, Ann. des Sc. Geol. tome vi. pi. 4. fig. 3.
It may be well to call attention to the identity of these two shells, separately figured and described in the two publications above mentioned. Mr. Seeley describes two varieties of his species ; but the figures are unfortunately very poor. They are, however, sufficiently recognizable ; and had Prof. Hebert seen them, he would probably not have described his A. valbonnensis as a new species. One advantage, however, has been derived from his oversight, namely the presence of an excellent figure of this variety in the Annales des Sciences Geologiques ; it might almost, indeed, have been taken from a specimen now in the Woodwardian Museum. I would suggest, therefore, that it hereafter stand under the name of A. coelonotus var. valbonnensis.
Ammonites acanthonotus, Seeley.
A. acanthonotus, Seeley, Ann. & Mag. Nat. Hist. 3rd ser. vol. xvi. p. 234, pi. xi. fig. 5.
After describing this peculiar form, Mr. Seeley remarks that a slight inflation extends all round one side of the whorl ; " but," he says, " from the near resemblance the shell has to A. glossonotus, I am not inclined to give that weight to the distortion it other- wise would have. The late Dr. S. P. Woodward, in 1862, regarded this shell as a monstrosity of A. lautus, Sow., a view with which I cannot agree."
In my opinion, however, there can be no doubt that Dr. Wood-
