BRACHIOPODA. 



151 



by him as C. Schaurothi. Dall suggests* that the species may represent a valid 

 subdivision of the genus Crania ; but while the interior remains unknown, and 

 the exterior is so similar to that of such species as C. setifera, C. seiigera and C. 

 spinifera, it would seem injudicious to assign it a distinct generic position. 



The generic term Pseudocrania, McCoy (Annals Nat. Hist., Second Series, 

 vol. viii, p. 387), was proposed in 1851. The following diagnosis was given in 

 British Palaeozoic Fossils, p. 187. 1855: 



" Shell slightly inequivalve, free; both valves regular, depressed, subconical, 

 unattached ; dorsal valve with or without a small cardinal area ; internally, 

 margin broad, flat, smooth or minutely striated concentrically; anterior pair of 

 muscular impressions much larger and more strongly marked than the posterior 

 pair ; pallial impressions numerous, linear, not interrupted along the middle. 



"This palaeozoic genus differs from the true Craniae in the following points: 



(1) Crania is attached by the substance of the dorsal valve, and exhibits 

 thereon an irregular scar ; both valves are free and regular in Pseudocrania : 



(2) in Crania the posterior or marginal pair of adductor muscles are always 

 larger and deeper than the medial or anterior pair ; the reverse is remarkably 

 the case in the present genus, which also has a smooth or minutely striated 

 margin, destitute of the strong granulation and punctures of most Craniae. 

 The Crania antiquissima, as given by Verneuil, may be taken as a type of the 

 genus, as also the following species " {Pseudocrania divaricata, McCoy.) 



The first of these typical species, the 

 Orbicula antiquissima, Eichwald,f = Crania 

 antiquissima, Verneuil,| as represented by 

 the latter author, shows a close similarity 

 to Pholidops, Hall, in the character of its 

 muscular scars. These are delineated as 

 two central impressions abutting against a 

 conspicuous posterior callosity, no evidence 

 appearing of any posterior marginal scar corresponding to the posterior ad- 

 ductors or divaricators of Crania. Mr. Davidson§ subsequently demonstrated 



Pseudocrania divaricata. 



After Davidson. 



ITIG. 70. Interior of upper valve : a, a'lituctors; J, ad- 



justors; m, mesenteric; r, divaricators; «, brachials. 



Fig. 71. Interior of lower valve. 



* Bulletin No. 8, U. S. National Museum, p. 19. 



t Silurian System in Esthland, p. 169. 1840. 



I G^nl. dc la Russ. de I'Europe, etc., p. 289, pi. i, tig. 12. 



§ Silurian Brachiopoda, p. 79. 



184.'). 



