148 MAZATLAN BIVALVES 
203. AVICULA STERNA, Gould. 
Proc. Bost. She Nat. Hist. Nov. 1851, vol. iv. p. 93 :—Mex. & 
Cal. Sheils, p. 31, pl. 16, f. 7.—C. B. Ad. Pan. Shells, p. 250, 
no. 392. 
Avicula Atlantica, Menke, Zeit. f. Mal. 1847, p. 187, no. 45; 
non Zam. 
‘Has the general appearance of A. semisagitta, Zam. but 
the wing is less oblique, and curves directly into the cauda 
without any sinus; the byssal sinus is deeper and much more 
acute, making a trapezoidal auricle. It most nearly resembles 
a Florida species; but in that the byssal angle is obtuse, the 
auricle triangular, and the cauda shorter.” Gould.* The hinge 
line is generally extremely long, but sometimes so short that 
the anterior are rather larger than the posterior auricles. Shell 
very inequivalve. Outer layer of shell dark chocolate, rarely 
slightly rayed with white. Surface almost smooth, with very 
fine concentric lines of growth. Epidermis in fine strongly ser- 
rated, closely folded laminz. Hinge teeth, card. 2-1, lat. 1-1. 
The pallial line is traceable from the large bilobed posterior 
adductor to the small anterior, situated just below the cardinal 
teeth. A peculiar species of Balanus is commonly found on 
this shell, and on the related W. Indian species. Many speci- 
mens of Discoporza intricata, and eggs of Gasteropods were 
also found attached. The smallest sp. is ‘05 in length ; the lar- 
gest 1°24. A normal sp. measures long. *98, lat. 2°5, alt. *42. 
One with short hinge EDS, @ Ss. eel ren OO: 
Hab.—Panama, Col. Jewett——Do.; very rare, attached to a 
small species of Gorgonia, at the low water mark of the 
spring tides; C. B. Adams.—Mazatlan; not uncommon ; 
LP’ pool Col. 
Tablet 676 contains a minute valve, ‘05 long, with the lateral 
tooth conspicuous.—677, 7 young pairs of different sizes, (one 
with egg cases) and a valve shewing spotted umbo.—678, 4 sp. 
adult.—679, 3 do. shewing interior.—680, 4 sp. different ages, 
with the ‘ear,’ ‘wing’ or ‘tail’ very much shortened; the 
larger with Discoporea intricata. 
* Dr. Gould’s ‘wing? appears to be the body of the shell; his ‘cauda’ what 
is by others called the wing or the ear. 
