little work, 'The Age of the Earth'[1], in which he devoted a portion of plate ii. to the illustration of some Lower-Carboniferous fossils from the Water of Leith. The name Axinus pentlandicus was adopted by Dr. Rhind for what I take to be two specifically distinct shells: one of these, fig. 6, was afterwards described and figured, without reference to Rhind's book, by Captain T. Brown, as Pachyodon pyramidatus, in a paper "On some new Species of the genus Pachyodon"[2]; the other, fig. a, is probably Brown's Pachyodon nucleus of the same paper. Brown's shells were found in "coal shale at Woodhall, on the north side of the Pentland Hills." It is almost unnecessary for me to observe that there is no coal shale at Woodhall. Fig. g of Dr. Rhind's plate is that of a Modiola, afterwards described by Capt. Brown as Avicula modioliforme in his 'Fossil Conchology,' where he also redescribed the two previous shells (Pachyodon pyramidatus and P. nucleus), but referred them to Unio[3]. In the previously quoted paper by the Rev. T. Brown, on the Carboniferous rocks of the Fifeshire coast, Mr. Salter gave a figure of a new species of Schizodus found by Mr. Brown to be plentifully dis- tributed throughout the Fifeshire lower series. The late Dr. Fleming obtained the same shell at Colinton, water of Leith, and would have referred it to Anatina attenuata, M'Coy; but Mr. Salter, on examining the hinge, pronounced it a Schizodus[4]. I have since described this shell as S. Salteri[5], in memory of my late friend; and when so doing I pointed out that it was probably identical with Pachyodon pyramidatus, Brown, and Axinus pentlandicus (fig. b), Rhind; but as both these authors appear to have figured imperfect examples of these shells, the matter must remain in a state of uncertainty, until an appeal can be made to their original specimens. Four species of bivalves are recorded in the Survey Memoir by Mr. Salter—the Avicula modioliforme, Brown, a thin-shelled species of Anthracomya? from the Wardie Shales, the Anthracosia? (Unio) nuciformis from the Burdiehouse Limestone, and an oval species of Myalina from the Clubbidean basement-beds of the Cement-stone group[6]. In a short paper of my own, published in 1875, I described the shell I have here mentioned under the name of Schizodus Salteri[7]. I was supplied by my friend Dr. Traquair with some good interiors; and by means of these, in conjunction with the original specimens kindly lent me by the Rev. Mr. Brown, the hinge-structure of the species was satisfactorily worked out. Dr. Traquair, at the same time, lent me specimens of the Modiola figured by Dr. Rhind, from which I was able to show its identity with Myalina crassa, Fleming. In a paper I communicated to the 'Annals and Magazine of Natural
