68 Proceedings of the Royal Physical Society. 



tomaria, have been raised to generic rank as Ptyehom^halus 

 by the late Professor Agassiz.* They are trochiform shells, 

 with a narrow band and short slit ; they are said to possess 

 an almost smooth surface, and a thick callosity covering the 

 umbilical region. Now, I have examined the type specimens 

 of both these species, and I think they can hardly be de- 

 nominated smooth shells, whilst the thick callosity is certainly 

 not well exhibited. The genus or section will probably, 

 however, be useful for the reception of the Palaeozoic im- 

 perforate PleuTotomarice in combination with some restriction 

 as to form. According to Dr Stoliczka,-f Ptychomphalits is 

 largely represented in the older deposits, but although the 

 above shells are found in the English Carboniferous limestone 

 I am not aware of their occurrence in Scotland. Judging 

 from the description of Cryptmnia^X by Deslonchamps, I 

 quite agree with Stoliczka in believing it to be identical with 

 Agassiz' Ptychomphahcs. The only other Palaeozoic sub- 

 division of PleuTotomaria known to me is the genus Trocho- 

 tremaria (De Eyckholt),§ and I quite fail to perceive any 

 difference between it and the before-mentioned Polytremaria. 

 The application of these subdivisions to our Palaeozoic 

 PleuTotomarim, and any further restriction of the genus can 

 only be effected by a thorough examination and revision of 

 the species, a work of much time and trouble. A very in- 

 teresting species of Pleurotomaria has been described from 

 the Lower Limestone series of Craigenglen, near Campsie, by 

 Mr J. Armstrong.il It is, I believe, exceptionally a Scotch 

 shell, and may perhaps belong to the section Ptychomphahis 

 {Ag?) — Cry2Jta:nia (Eg. Deslonchamps). 



The genus Murchisonia was established by Messrs d'Archiac 

 and De Verneuil H for Palaiozoic Shells, many of which had 

 been previously referred to Buccinum, Ttirritclla, etc. The 



* German Edition of Sowerby's Min. Con. 

 t Cretaceous Gasterop. of India, p. 382. 

 + Bull. Soc. Linn, de Normandie, 1865, ii., p. 424. 

 § Jour, do Couchol, 1860, viii., p. 186. 



II Description of two new species of shells from the Carboniferous Lime- 

 stone of Clydesdale (Trans. Glasgow Gcol. Soc, ii., pt. 1, p. 74). 

 H Bull Soc. Gcol. de France, 1841, xii., p. 159. 



