Spondylus. 
MOLLUSCA. ARCADJE. 
397 
Gen. spondylus.-— S hell 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 striae. 
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 squamae placed at 
about half an inch distant, these striae being separated by from six to nine 
small granular strife.” 
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. inflata — 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, 16, 17* P* inf. Sower. Min. Conch, t. ccccix. f. 2. — 
Chalk Marl. 
AUCAD.^. 
Gen. XCVIII. ARC A. — 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. No£6, Lmn. Syst. i. 1140. — A. tortuosa, Penn. Brit. Zool. iv. 
97* — A. Noge, Don. Brit. Shells, t. clviii. f. 1, 2. Mont. Test. Brit. J39. 
Turt. Biv. Brit. 166 — Western coast of England and Guernsea, rare. 
Shell about half an inch long, a little more in breadth ; rufous, Avith dark 
zigzag bands, rounded at the longest end, angular at the other, to which the 
incurved beaks approximate. 
401. A.fusca . — Shell oblong, decussated, angular at the ante- 
