CRANIA. 181 



or pear-shaped, adjacent in front and slanting outwards, situate immediately 

 behind the apex, and one-seventh of the shell in length. Divaricator scars 

 rather larger and more oval than the occlusors, concave, elongate, not slanting, 

 apparently bisected longitudinally, situate at the postero-lateral corners, and 

 touching the inner edge of the marginal rim. Surface (of cast) traversed by an 

 irregular transverse ornament, reproduced from the organism to which it was 

 attached. 



Size. — Length 13 mm., width 12 mm., depth 7 mm. 



Localities. — In the Barnstaple Athenaeum is a specimen on a slab with Productus 

 prselongus, Bhynchonella Partridgiss, &c. Though its locality is not stated, it is 

 clearly from the equivalent to the Top Orchard beds. A doubtful specimen is in 

 the Porter Collection from Pilton, and another in my Collection from Ashhill 

 Quarry. 



Bemarlcs. — The figured specimen is indistinct, especially in consequence of its 

 having irregular ridges assumed from some other organism on which it was 

 parasitic. Davidson 1 notes that the free valves of the Carboniferous Craniae are 

 sometimes similarly marked. The broad marginal concavity seems to indicate a 

 massive shell, and the concave marks in the cast show that in the shell the 

 muscle-scars were very convex. 



In 1896 I referred this shell to Craniella Meduanensis, (Ehlert; 2 I am inclined 

 now to think that there are probably, not sufficient grounds for this identification ; 

 the muscular impressions appear to be smaller and differently shaped, and there 

 appears something in the nature of a border. Moreover, Mons. (Ehlert, judging 

 from a photograph submitted to him, regards it as a Craniella of the group of 

 Meduanensis, but distinguishable by its contour, the situation of the muscles, and 

 the position of the summit. 



To the Carboniferous Crania quadrata, M'Coy, sp., 3 it also appears somewhat 

 similar; but it is distinguished by the anterior position of its vertex and its 

 occlusor scars, and by the more transverse shape of its divaricator scars. 



Of Crania proavia, Goldfnss,* I have only been able to find figures and 

 descriptions of the lower or fixed valve, and have therefore been unable to 

 compare it. In shape it would seem to have been more rectangular and 

 transverse. 



1 1861, Davidson, ' Brit. Toss. Brach.,' vol. ii, pt. 5, p. 195. 



2 1888, (Ehlert, ' Bull. Soc. Btud. Sci. Angers,' (1887), p. 38, pi. x, figs. 1—1 g. 



3 1844, M'Coy, ' Synops. Carb. Boss. Irel.,' p. 104, pi. xx, fig. 1. 



* 1853, Schnur, ' Palaeontographica,' vol. iii, p. 230, pi. xliii, figs. 9 a, b ; and 1871, Kayst-r, 

 'Zeitsch. Deutsch. Geol. Gesell.,' vol. xxiii, p. 641, pi. xiv, fig. 6. 



