CRANIA. 11 



Obs. The only specimens I have seen and figured in my Plate I. are from the 

 collection of Mr. Sowerby, and would appear to have been found in the Kim clay, 

 Shotover, Oxon. Fig. 3a is an enlarged illustration. Among the recent species we find 

 more than one longitudinally striated. 0. Cummigii, &c. 



Genus — Crania, Retzius. 1781. 



Shell unequivalve, circular or subquadrate, more or less irregular, entirely or partially 

 attached by the substance of smaller valve to rocks, corals, and other submarine bodies ; 

 upper valve conical, with lateral or subcentral vertex, without hinge or ligament ; lower or 

 attached valve thickest, often irregular, due to the nature of the object to which it is fixed ; 

 surface strongly punctured or spongy ; four circular depressed, or produced muscular 

 impressions in each valve, the first two, formed by the adductor muscles, are situated near 

 the cardinal edge, the other pair are approximated and placed near the centre, behind 

 which a central prominence is sometimes seen ; the space between these and the wide, 

 thicker, granular margin surrounding the shell, is divided by the digitated genito- 

 vascular impressions; arms fleshy, free only at their extremities ; no calcareous supports. 



Obs. We are only acquainted with two British Oolitic cranias, C. Antiquior and 

 C. Moorei, and, unfortunately, of these only one of the valves has been hitherto discovered. 



* 



5. Crania Antiouior, Jelly. Plate I, figs. 4 — 8. 



Crania antiquior, Morris. Catalogue, 1843. 



— — Dav. London Geol. Journal, vol. i, pi. 18, figs. 21 — 25. 1847. 



— — Bronn. Index Palseont., p. 342. 1849. 



— — VOrb. Prodrome, vol. i, p. 316. 1849. 



Diagnosis. Shell suborbicular, irregular, the lower valve only known ; it varies 

 in form, some specimens being almost flat, others more or less concave, and even occasion- 

 ally patelliform. The muscular impressions are four, more or less ; strongly marked in 

 different examples ; the two posterior are generally larger and more widely separated than 

 the two anterior ones, which latter usually touch, and are also less circular in form than 

 the upper, and depressed in the centre. In most examples a strongly-marked ridge is 

 seen extending in the mesial line, from the junction of the lower muscular impressions to 

 the margin of the shell, as displayed in fig. 8. The very peculiar spongeous structure, 

 characteristic of the genus Crania, is well marked. In form and general appearance this 

 species somewhat approaches Crania abnormis of the tertiary period. Length 7, breadth 

 6^ lines ; some specimens are almost square. From the appearance of the exterior this 

 Crania would not seem to have been much attached. 



Obs. A very extensive series of specimens of this species, forwarded to me by 



