104 DEVONIAN FAUNA. 



margins, especially the inferior margin. Surface covered by about forty very 

 distant, fine, sharp, elevated, erect, concentric threads, which occasionally become 

 slightly irregular, are closer and smaller on the supero-lateral parts, and are 

 crossed in the marginal regions by numerous microscopic radiating lineations, 

 which, however, may possibly have been induced by other causes instead of being 

 a true testaceous ornament. 



Size. — About 24 mm. long, 22 mm. high, and 3 mm. deep. 



Locality. — In the Barnstaple Athengeum is a fine but not very perfect example 

 from Bradiford. Phillips describes his shell from South Petherwyn. 



BemarJcs. — Our figured specimen exactly agrees with Phillips's figure, so that 

 there can be no doubt of its identity. As its umbo and hinge are hidden, there is 

 little direct evidence as to its genus. In general shape it closely mimics shells 

 like Astarte, but its resemblance to adjacent species leaves little doubt that it 

 belongs to the present genus. 



Its transverse ornament is precisely similar to that of Gt. antiqua, Sowerby, sp., 

 and it is quite within the range of possibility that further specimens might 

 afford ground for regarding it as the aged form of a variety of that variable shell. 



The present form has, however, such a distinctive, obliquely subquadrate 

 shape, that, judging from what we know of it at present, there appears to be just 

 grounds for believing Phillips to be right in regarding it as a distinct species. 



Affinities. — Paracijclas lirata, Conrad, as given by Hall,^ is identically orna- 

 mented, and approaches it in shape, but is more convex, and has much fewer ribs, 

 and could claim kinship only on the assumption that the present species did not 

 belong to the NiLCulidse. 



6. Ctenodonta ? TENSA, n. sp. Plate XII, figs. 8, 9 ? 9a? 



? 1842. NucuLiTES SULCATINA, ConraiL Journ. Acad. Nat. Sci. Philad., vol. viii, 



p. 250, pi. XV, fig. 10. 

 ? 1881. Leda pebdentata, Barrande. Syst. Sil. Bohem., vol. vi, pi. cclxx, fig. 2, 



1-9. 



? 1885. PALiEONEiLO SULCATINA, Hall. Pul. N. Y., vol. V, pt. 1, No, 2, p. 347, 



pi. I, figs. 42—46. 



JDescrijytion. — Shell of moderate size, convex, ovoid, very transverse, but 

 narrower behind than in front. (Umbo unseen but apparently low, indistinct, 

 and situated near the anterior end.) Hinge-line apparently very long, gently 



1 1885, Hall, ' Pal. N. T.,' vol. v, pt. 1, No. 2, p. 441, pi. Ixxii, figs. 2—19 ; and pi. xcv, fig. 19. 



