CTENODONTA. 103 



appears from our figure, which was carefully drawn from the very indistinct type- 

 specimen and its cast. 



Affinities. — From Gt. lirata it differs in its flatness and even contour, its smaller 

 and plainer posterior slope, and its finer strige. 



Ct. elli])tica is much less transverse, but the larger specimens of the present 

 shell seem gradually to approach it, though still differing in having a narrow posterior 

 margin, and in not having the strige so broadly parallel to that margin. 



The North Devon shell, referred to Nuculites latissimus, Phillips, sp., is more 

 transverse, less ovate, less truncated behind, and more finely striated. 



Palseoneilo filosa, Conrad,^ is a narrower shell with a much wider posterior 

 slope and finer strise. 



Sangimiolaria gibbosa, Goldfuss,^ not Sowerby, which Beushausen^ refers to 

 this genus, is rather similar in shape and markings, except that, according to the 

 latter author, the ridges are numerous and crowded near the margins, and the shell 

 shorter and the umbo higher. 



The Carboniferous Gt. Hallii, Barrois,* agrees in shape, but differs in its less 

 defined and regular ornament. 



Gucullsea antiqua, Sowerby/ the type of which is in the Museum of the 

 Geological Society, is almost exactly the same in shape, but it has a long stout 

 clavicular ridge, is more convex, and is described as smooth, Sowerby does not 

 appear to unite the two shells, which he places in different genera, though giving 

 them the same specific name. 



4. Ctenodonta? elliptica, Phillips, sp. Plate XIII, fig. 6. 



ISil. PuLLASTBA ELLIPTICA, Phillips. Pal. Foss., p. 35, pi. xvii, fig. 54. 

 1893. Ctenodonta elliptica, Collins. Trans. Eoy. Geol. Soc. Cornwall, vol. xi, 



p. 36. 



Description. — Left valve of moderate size, flat, oblique, subcircular. Umbo 

 somewhat anterior, flat, depressed, small and hardly defined. (Apex and hinge- 

 line unseen.) Anterior margin broad, slightly convex. Inferior margin gently 

 and regularly convex. Posterior margin convex below, straight and oblique 

 above. Contour of back nearly flat, but sinking suddenly and rapidly close to the 



1 1885, Hall, • Pal. N. T.,' vol. v., pt. i, No. 2, p. 343, pi. xlix, figs. 33—38. 



2 1834-40, Goldfuss, ' Petref. Germ.,' vol. ii, p. 279, pi. clix, fig. 10. 



3 1895, Beushausen, ' Abbandl. k. Preuss. Geol. Landes.,' n. s., pt. 17, p. 83, pi. vi, fig. 16. 

 * 1882, Barrois, • Mem. Soc. Geol. Nord,' vol. ii, No. 1, p. 339, pi. xvii, figs. 3—3 c. 



5 1839, Sowerby, in Murchison's ' Sil. Syst.,' p. 602, pi. iii, figs. 1 h and 12 a. 



