Spondylus. MOLLUSCA. ARCADE. 397 



Gen. SPONDYLUS.— Shell eared, beak of the under valve 

 produced, with an exposed oblique truncation, having a 

 longitudinal groove ; hinge of two teeth, with an interme- 

 diate groove for the reception of the internal ligament. 



1. S. radula. — Mr Parkinson refers to a shell of this species (of Lamark, 

 from Grignon), which he suspects to have been from "Worcestershire. " It is 

 slightly eared, and the inferior valve is marked with rough longitudinal stria?. 

 It is rough, oblique, and of an oval orbicular form. The stronger and most 

 raised of the striae of the lower valve have small spinous squama? placed at 

 about half an inch distant, these striae being separated by from six to nine 

 small granular striae." 



Gen. PLICATULA. — Shell destitute of ears ; narrow at the 

 base ; the opposite margin rounded and plaited ; beaks un- 

 equal entire ; teeth two, with an intermediate pit for the 

 subinternal cartilage. 



1. P. spinosa. — Ovate depressed, spinose; margin entire; spines adpressed ; 

 smallest on the deep valve — Harpax, Park. Org. Rem. iii. 221. t. xii, f. 14. — 

 P. spin. Sower. Min. Conch, t. ccxlv — In Lias. 



2. P. pectinoides — Oblong, ovate, curved, gibbose when old ; longitudinal 

 ridges numerous, furnished with depressed spines ; free valve externally con- 

 cave. — Sower. Min. Conch, t. ccccix. f. 1. — Chalk Marl. 



3. P. infiata — Suborbicular, gibbose, rather smooth, furnished with a few 

 ridges and depressed spines ; both valves convex. P. spinosa, Mant. Geol. 

 Suss. 129. t. xxvi. f. 13, 1G, 17- P. inf. Sower. Min. Conch, t. ccccix. f. 2.— 

 Chalk Marl. 



ARCADiE. 



Gen. XCVIII. ARCA. — Shell transverse ; beaks remote ; 

 teeth numerous, enlarging from the middle, but without 

 lateral teeth ; ligament external. 



400. A. Noce. — Shell oblong, decussated in a punctured man- 

 ner, angular at the anterior side, with the upper margin trans- 

 versely elongated, sinuous and open. 



Musculus striatus, List. Conch, t. ccclxviii. Borl. Corn, cclxxvii. t. 28. 



f. 16 A. Nose, Linn. Syst. i. 1140 A. tortuosa, Penn. Brit. Zool. iv. 



97 A. Noae, Don. Brit. Shells, t. clviii. f. 1, 2. Mont. Test. Brit. J 39. 



Turt. Biv. Brit. 166 Western coast of England and Guernsea, rare. 



Shell about half an inch long, a little more in breadth ; rufous, with dark 

 zigzag bands, rounded at the longest end, angular at the other, to which the 

 incurved beaks approximate. 



401 . K.fusca. — Shell oblong, decussated, angular at the ante- 



