SPIRIFERIDtE. 



137 



of about equal width ; the valves are crossed at intervals by sharp concentric slightly 

 raised undulating lines. 



Length 5, vt^idth 6, depth 2^ lines. 



Obs. Sowerby describes this pretty little species as a beautiful fan-like shell, easily 

 recognisable by its convex ventral, and almost flat dorsal valve. In Great Britain it 

 occurs chiefly in the condition of external impressions and internal casts. The cast of 

 the flattened dorsal valve shows an elongated slit, for a tooth, on each side of the beak 

 between which a small triangular cardinal boss extends to a short distance, with deeper 

 pits on either side. At the base of this prominence commences a well-pronounced 

 distinct median sulcus, which extends to about half the length of the valve (indicating in 

 the shell the presence of a small median ridge) ; and on either side of the sulcus may 

 be seen two impressions referable to the adductor or occlusor muscle. In the convex 

 cast of the ventral valve on either side of the beak there exists a short diverging slit 

 (produced by the dental lamina), and a little further on the pits left by the teeth. The 

 muscular impressions are obscurely indicated. 



At p. 202 of his ' Brit. Palaeoz. Foss.' Prof. M'Coy states, " As some modern writers 

 have referred this shell to the genus Orthis, I have taken great pains to ascertain the 

 characters of the hinge, as the obvious absence of the puncturing in the tissue of the shell 

 rendered the reference to Orthis very doubtful in my mind ; and I have convinced myself 

 that there is no cardinal area whatever, but that the beak of the entering (dorsal) valve is 

 simply pointed, hollow, and so much incurved only as to leave a wide triangular foramen 

 beneath it ; the hinge-characters, therefore, warrant the placing this singular shell in 

 Hemithyris, with which also its tissue is identical." 



Prof. Hall and Mr. Billings place Atrijpa? hemispharica of Sowerby in the first- 

 named author's genus Leptoccelia ; and although it is very probable that the shell is 

 neither an Atrypa, Terebratula, nor Mhynchonella 

 {Hemithyris), and that we have not yet obtained a 

 permanent home for it, still, as the interior of the 

 species is imperfectly known, and we have no positive 

 certainty that it was similar to that of Leptoccelia 

 flabellites — the type of Hall's genus — it will, I think, 

 be more prudent to follow Messrs. J. de C. Sowerby, LeptocosUa flabeiutes, after j. Hairs figures. 

 Salter and others, in leaving it for the present with ^- i"*"*"'^ «f •^"■'^^i ^^i^^' ^^''^'"^ '''^ 



_ ^ cardinal process, crura, and crural plate, re- 



Atrypa. Having made moulds in gutta-percha from stored from cavities seen in a cast, 

 a number of internal casts of the dorsal valve of b. interior of the ventral vaive. 

 specimens from the May Hill Sandstone of Anker- 

 dine, obhgingly collected for me by Dr. Holl, and where the species occurs by 

 millions under the condition of external impressions and internal casts, I am able 

 to detect several differences from what we observe in the cast of the same valves 

 of Leptoccelia flabellites, and which I will endeavour to describe. In the inside 



18 



