MAZATLAN BIVALVES 147 



201. Pinna lanceolata, Sotv. 



Proc. Zool. Soc. 1835, p. Si— Hani JDescr. Cat. p. 256. 



Shell, when extremely yoiing, nearly smooth -nitli a very 

 long liinge line, but mucli shortened posteriorly : gradually 

 developing radiating ridges, 8-10 in the adult, which become 

 furnished with regu.lar 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, long. 4"2, led. 1"7, alt. (with spines "77, without) 

 •28. 

 Hab. — Puerto Portrero ; in sandy mud, 13 fm. ; Cuming. — 



Mazatlan ; in fine sand, not ujicommon ; 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 Pbugosa, Sow. 



Proc. Zool. Soc. 1835, p. 84.— Ja«7. JDescr. 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, 

 verj" 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 ; verj' long and nari'ow, ventral 

 part not inflated ; with about 6 strong ribs, traceable from 

 the umbos, and scarcely 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 Key, Bay of Panama, on sand banks, Cuming. — 



P Mazatlan ; very rare ; L'liool Col. 



Tablet 675 contains the smallest and the largest specimens. 



Genus AVICULA, Klein. 



Avicula, Klein, 1753 -.—Brtig. 1789 -.—Lam. 1799. 

 Pteria, Scopoli, 1777 -.—Gray, 1847. 



