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 fiat; 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 Coelospira ; and the socket walls, which are also the bases 
of the crura, are short, but prominent and elevated, bordering deep and narrow 
* Palseontology of New York, vol. iv, pp. 409-411, pi. Ixii. 
