152 
PALAEONTOLOGY OF NEW YORK. 
the existence of these posterior scars in the Russian species and was inclined 
to regard the specific difference in the Orbicula antiquissima and Pseudocrania 
divaricata as not great. With Pholidops, therefore, they can agree only in the 
fact of being unattached shells, the two distinct pairs of muscular impressions 
on the inside and, in P. divaricata, the posterior beak and radiating ornamenta¬ 
tion on the exterior, separating them definitively from this genus. The features 
upon which McCoy proposed to separate these species from Crania should not 
be given too great importance; the unattached habit of the shells throughout 
their existence may prove of value as a basis for a section of the genus Crania, 
but the fact that the central muscular impressions are often larger than the 
anterior, will not hold good for these forms only, as it is often seen in the 
American species of Crania. We are disposed to agree with Mr. Davidson in 
regarding Pseudocrania as synonymous with Crania. Pseudocrania divaricata 
is from the Bala limestone and Llandeilo flags; P. antiquissima from the Vagina- 
ten-kalk, near St. Petersburg. 
Eichwald, # in 18-60, proposed to designate the species, Orbicula antiquissima, 
by the term Palaeocrania, as it differs from Pseudocrania divaricata in -the cen¬ 
tral position of the beak and the concentric markings of the shell. This 
proposal however is illegitimate, as 0. antiquissima was the first type of Pseudo¬ 
crania and therefore is not available as the basis of another genus. 
Should these two species not prove congeneric either with each other or with 
Crania, Eichwald’s term will, under any circumstances, prove inadmissible. 
When the Orbicula antiquissima becomes better known it may furnish a satisfac¬ 
tory foundation for Pseudocrania as a genus.f 
* Lethaea Rossica, vol. i. p. 909. 
t The only American species which has been referred to Pseddocrania is the Crania ( Pseudocrania) 
anomala of A. W tnchell, from the Hamilton group (Rept. Grand Traverse Region of Michigan, p. 92. 1866). 
By the favor of Professor Winchell we have been allowed to examine specimens agreeing with the original 
description, and are compelled to pronounce the name a misnomer, as the species is a well defined strepto- 
rhynchoid. 
