BRACHIOPODA. 139 



illustration of V. pustulosa in 1867* Its general external resemblance to 

 Tropidoleptus and its almost universal association with that genus in 

 Devonian faunas have led to a tacit concession, on the part of some authors, 

 of structural relations in the two genera. All observations upon Vitulina 

 have heretofore been based upon separated valves or casts of their interiors. 

 Specimens in which the valves are retained in their normal position are of 

 extreme rarity, and it is from such an example, obtained in the Hamilton 

 shales of Alden, New York, that we have succeeded in demonstrating the 

 species to be spiriferous, and that its structural characters ally it closely 

 to the genera which have just been discussed. The distinctive features of the 

 genus may be summarized as follows : 



Shell of rather small size ; plano-convex in contour, transverse, the hinge- 

 line making the greatest diameter of the valves. The pedicle-valve is convex, 

 its umbo scarcely elevated and its apex not prominent or incurved. A cardinal 

 area is highly developed, and is divided medially by an open, triangular 

 delthyrium, which bears no traces of deltidial plates in any condition that has 

 been observed. The delthyrium is very wide, its base covering more than 

 one-third the extent of the hinge-line. The teeth are blunt, thickened, and 

 not supported by dental plates. The scar of the pedicle-muscle is distinctly 

 defined, but those of the other muscles are obscure in their limitation. Under 

 the most favorable preservation, there appears a posterior flabelliform pair, 

 situated just in front of the pedicle-scar, and in advance of these a median 

 scar enclosed by two anterior diductor impressions. There is, at times, a low 

 median ridge, which is purely muscular in its origin. 



The brachial valve is depressed-convex or flat ; it bears a narrow cardinal 

 area coextensive with that on the opposite valve. The delthyrium is wide and 

 open, and when the conjoined valves are viewed from behind, the cardinal pro- 

 cess and socket walls are clearly seen through the wide pedicle-passage. The 

 former of these, the cardinal process, is a straight, simple apophysis, like that 

 in Anoplotheca and C(EL0Spira ; and the socket walls, which are also the bases 

 of the crura, are short, but prominent and elevated, bordering deep and narrow 



* Palaeontology of New York, vol. iv, pp, 409-411, pi. Ixii. 



