338 MALACOZOA. TROPIOPODA. LAMELLIBRANCHIATA. 



1. Pectunculus Glycimeris, Ribbed Pectunde. 



Shell suborbicular, oblique, anisomeral, slightly an- 

 gulate at the longer end, obscurely ribbed, with minute 

 divergent striae decussated by concentric striae ; the ex- 

 terior whitish with diversiform subundulated red mark- 

 ings, the interior white, the margin crenato-dentate. 



Shell subovato-orbicular, somewhat oblique ; with the um- 

 bones incurved and pointed, the valves moderately convex, 

 the anterior end subangulate ; the surface covered, especially 

 toward the margin with short dense silky dark-brown hairs, 

 under which it is marked with faint divergent ribs, with inter- 

 vening sulci so narrow as to resemble cbinks or cracks in the 

 shell, and very numerous minute, undulated striulae, decus- 

 sated by concentric striae ; the colour whitish, variegated with 

 angular and undulated light-red markings ; the hinge margin 

 broad, with about twenty-two oblique teeth and corresponding 

 depressions ; the margin dentato-crenate, the teeth and inter- 

 spaces corresponding to the costae. Length two inches and 

 a twelfth and a-half, height an inch and eleven-twelfths. 



A single valve, from the Bay of Peterhead, sent in January, 

 1843, by Roderick Gray, Esq. This appears to be the true 

 Glycimeris of Linnaeus, not Pectunculus pilosus, which is 

 much more convex, and differently marked. 



Area Glycimeris, Linn. Syst. Nat. 1143. Area Glycimeris. 

 Penn. Biit. Zool. iv. PI. 58. f. 58. Pectunculus Glycimeris. Turt. 

 Brit. Biv. 171. PL 12. f. 1. 



FAMILY V. CYCLADINA. P. 208, 245. 



GENUS 2. PISIDIUM. P. 209, 248. 

 Pisidium dmnicum. River Pisidium. 



Shell obliquely ovate, ventricose, thin, glossy, deeply 

 concentrically striate, with more marked growth-lines ; 

 the umbones tumid, obtuse, striated at the apex, much 

 nearer the anterior end; the dorsal slope declinate, a 

 little convex ; both ends rounded, the anterior much 

 narrower; the colour olivaceous. Amnicus, living in 

 rivers. 



Shell ovate, somewhat oblique, broadly rounded anteriorly, 

 narrowly rounded behind ; very convex, with the umbones 

 large, convex, striated, and placed much nearer the anterior 



