MAZATLAN BIVALVES 147 
901. PINNA LANCEOLATA, Sow. 
Proc. Zool. Soc. 1835, p. 84.—Hanl. Deser. Cat. p. 256. 
Shell, when extremely young, nearly smooth with a very 
long hinge line, but much shortened posteriorly: gradually 
developing radiating ridges, 8-10 in the adult, which become 
furnished with regular rows of long, almost tubular spines, 
extremely thin, light horny brown, ventral part swollen and 
smooth, with the margin rounding off posteriorly till it meets 
the dorsal line at right angles. Hinge line often incurved 
near the umbos. The smallest specimen found is 1°75 long ; 
the largest, Jong. 4°2, (dt.1°7, alt. (with spines ‘77, without) 
S28: 
Hab.—Puerto Portrero; in sandy mud, 13 fm.; Cwming.— 
Mazatlan ; in fine sand, not uncommon ; L’pool Col. 
Tablet 670 contains 3 sp. very young.— 671, 2 do. older, with 
few rows of spines developed.—672, 4 do. ordinary state.—673, 
2 do. crowded with tubercles.—674, 1 do. distorted growth. 
202. Pinna P RvUGOsA, Sow. 
Proc. Zool. Soc. 1835, p. 84.—Hanl. Descr. Cat. p. 256. 
P. rugosa, jun., teste Cuming. 
About a score of specimens were found with P. lanceolata, 
presenting the following characters. Shell extremely thin, 
very light horn coloured, transparent, glossy, with the cell- 
structure so large as to be visible to the naked eye, giving a 
peculiar texture to the surface ; very long and narrow, ventral 
part not inflated; with about 6 strong ribs, traceable from 
the umbos, and searcely ceasing at the ventral part, armed 
with large, distant, nearly tubular spines. The smallest speci- 
men is 1°9 long; the largest, long. 4°8, lat. 2°, alt. (with 
spines 1°2, without) *64. 
Hab.—Isle of Rey, Bay of Panama, on sand banks, Cuming.— 
P Mazatlan; very rare; L’pool Col. 
Tablet 675 contains the smallest and the largest specimens. 
Genus AVICULA, Klein. 
Avicula, Klein, 1753 :— Brug. 1789 :—Lam., 1799. 
Pteria, Scopolt, 1777 :—Gray, 1847. 
