MUSEUM OF COMPARATIVE ZOOLOGY. 39 



1822. — Blainville, Diet. Sci. Nat., XXXII, p. 304, 1824. Ibid., 

 XXXVI, p. 291, 1825. — Defrance, Ibid., XXXVI, p. 293, 1825. 



= Patellites (sp.) Schlotheim, Petref., I, p. 114 ; II, p. 108, 1820-1823. 



= Patella (sp.) Brongniart, Tabl. des Terr., p. 419, 1829. 



= Calyptrcea (sp.) Goldfuss, Alberti, Betr., Mori. Trias , pp. 54, 93, 1831 * 

 (fideBRONN, Ind. Pal.). 



= Terebratala pars, Schweig., Naturg., p. 690, 1820 * (fide Gray, An. Phil.). 



Not Orbicula Cuvier, Tabl. Ele'm. R. An., p. 435, 1798. — Lamarck, Hist. 

 An. s. Vert., I, VI, Part I, p. 242, 1819. — Deshayes, Enc. Me'th. Vers, 

 III, p. 668, 1832. — Schumacher, Essai, p. 55, 1817. — Thomas 

 Brown, Conch. Textb., p. 107, Ed. V, 1839, nor Macgillivray, 

 Ibid., Ed. IX, p. 123, n. d. (= Crania). 



Subgenus DISCINA (Lam.) Dall. 



Shell of rather solid texture, with a considerable amount of calcareous 

 matter iu it ; no signs of punctation to be seen with a half-inch objective. 

 Valves convex, the lower valve varying in amount of convexity with its 

 habitat, but always more or less inflated. A small, sharp, longitudinal 

 septum rises from the centre of the lower valve, of a subtriangular shape, 

 covering and hiding a small tubular perforation of the apex of the shell. 

 This perforation is very oblique, and from its internal opening a groove 

 extends backward nearly half-way to the posterior border of the shell 

 inside. The anterior muscular scars meet in front of the septum and form 

 a semilunar elevation with the points directed backward. The posterior 

 scars in the lower valve are small and widely separated. On the external 

 surface the foramen appears nearly in the middle of the shell, and the fur- 

 row is continued anteriorly for a short distance. (There is no furrow in 

 my specimens outside behind the foramen, which is the only point of differ- 

 ence from Sowerby's figures.) 



Upper valve convex, apex subcentral ; a slight median longitudinal 

 callus internally. There is no strongly impressed disk about the foramen 

 as in Discinisca, though slight traces of a differentiated area exist there. 



Type Discina striata Schcm. sp. 



Syn. Crania (/3) striata Schumacher, Essai, p. 102, pi. xx, figs. 1 a-f, 1817 (not 

 of Defrance). Habitat? 

 Crania radiosa Gld., Moll. U. S. Expl. Exped., p. 465, figs. 480, a-c, 1852. 

 Hab. Cape Palmas, Liberia, not Rio. 



** Not Orbicula striata Sby., in Murch. Silurian Syst., tab. v, fig. 21, 1S39, and Siluria, 

 pi. xx, fig. 3, 1859. This species is perhaps identical with Discina Verneuilii Dav., 1848; 

 but if it should prove distinct, it must have anew name, as that of Schumacher has many 

 years' priority. It occurs in the upper Ludlow rocks of Shropshire, and the D. Ver- 

 neuilii in the Wenlock limestone of England. 



