Ceiopus. MOLLUSCA. SESSILIA 377 



fissure, to which the peduncle adheres ; inside thickened round the fissure, 

 with a vertical grooved tooth. I have been induced to give this species 

 (which was found attached to stones used as ballast, and brought to Lam- 

 beth) its present place, but even without good proof of its British origin, for 

 the purpose of rectifying some strange mistakes in nomenclature, which have 

 been committed in reference to this and the following genus. The specimen 

 in my possession I owe to the kindness of Mr J. Sowerby. 



EXTINCT SPECIES. 



1. jy.rejlexa — Shell subelliptical, most pointed towards the' back, polish- 

 ed ; upper valve rather convex, with the vertex near the posterior margin ; 

 lower valve flat, with a nearly central vertex, the margin reflected ; sinus for 

 the byssus lai-ge, elongated. — Orbicula ref. G. B. Sower. Zool. Journ. ii. 321. 

 t. xi. f. 7. Miu. Conch, t. Dvi. f. 1 — Lias. 



2. D. Humphreisiana. — Conical, orbicular, marked with diverging striae ; 

 apex elevated, rather excentric, obtuse. — Orbicula Humph. Sower. Min. 

 Conch, t. Dvi. f. 2 Oolite. 



3. D. granulata. — Conical, orbicular, marked with granulated radii ; apex 



elevated Orbicula gran. Soicer. Min. Conch, t. Dvi. f. 3, 4.— Oolite at An- 



cliffe. 



Gen. XCIII. CRIOPUS. (Poll)— Under valve cemented to 

 stones ; upper valve depressed, the inside with two round- 

 ed marginal, and two arculated subcentral muscular im- 

 pressions. 



370. C. anomalus. — Shell rough, with obsolete concentric 

 wrinkles, apex prominent. 



Patella anomala, Mtill. Prod. 23?. No. 2870. Zool. Dan. t. v. f. 1-8 



Patella distorta, Flem. Edin. Ency. vii. 65. t. 204. f. A.— Mont. Linn. 

 Trans, xi. 195. t. xiii. f. 5. — Orbicula Novegica, Lam. Hist. vi. pt. i. 

 242. — Crania personata, G. B. Sowerby, Linn. Trans, xiii. 471. t. 26. 

 f. 3 — Criopus anomalus, Flem. Phil. Zool. ii. 499.— Discina ostreoi- 

 des, Turt. Biv. Brit. 238 — On loose stones from deep water, Zetland. 



Length /jths, breadth /gths, and height j^ths of an inch ; brown ; sub- 

 quadrangular, wrinkled by the lines of growth, apex subcentral, inside punc- 

 tated ; lower valve very thin, in young specimens membranaceous ; four mus- 

 cular impressions. Muller states, that the spiral arms are white. Accord- 

 ing to Mr G. B. Sowerby the C. turbinatiis, the type of the genus Criopus of 

 Poll, and Orbicula, of Lamark, from the Mediterranean, differ only in the 

 greater thickness and irregularity of the lower valve. A specimen referred 

 to the Mediterranean species has been found by Mr Miller, at Bristol, on 

 the Area Noae. It is probable that the genus Crania of Lamark is nearly 

 related to, yet distinct from, the Criopus. 



EXTINCT SPECIES. 



1. C. Parisiensis — Suborbicular, depressed ; upper valve thin, obscurely 

 granulato-spinose, smooth in the centre ; lower valve thick, with the margin 

 much elevated, and of a conspicuously cellular structure. — Crania Par. Sower. 

 Min. Conch, t. 408 On Echini in Chalk. 



