148 MAZATLAN BITALVES 



203. AVICULA STEENA, Gould. 



Proc. Bo.it. Soc. Nat. Hist. Nov. 1851, vol. iv. p. 93 :—Mex. Sf 

 Cal. Shells, p. 31, pi. 16, f. 7.— C. B. Ad. Pan. Shells, p. 250, 

 no. 392. 



Avicula Atlantica, Menhe, Zeit.f. Mai. 1847, p. 187, no. 45 ; 

 non Lam. 



"Has the general appearance of A. semisagitta, Lam. 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 ina?quivalve. Outer layer of shell dark chocolate, rarely 

 slightly rayed with white. Surface almost smooth, with very 

 fine concentric lines of gi-owth. Epidermis in fine strongly ser- 

 rated, closely folded lamina^. Hinge teeth, card. 2-1, lat. 1-1. 

 The pallial line is traceable from the large bUobed jjosterior 

 adductor to the small anterior, situated just below the cardinal 

 teeth. A peculiar species of Balanus is commonly foimd on 

 this shell, and on the related W. Indian species. Many speci- 

 mens of Discoporaja intricata, and eggs of Gasteropoda were 

 also found attached. The smallest sp. is '05 in length ; the lar- 

 gest 1"24. A normal sp. measures hug. '98, lat. 2 '5, alt. '42. 



One with short hinge „ 1-23, „ 1"7, „ •59. 



Mab. — Panama, Col. Jeicett, — 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 ; 

 IS pool Col. 



Tablet 676 contains a minute valve, '05 long, with the lateral 

 tooth conspicuous. — 677, 7 young pairs of diflerent sizes, (one 

 with egg cases) and a valve shewing spotted umbo. — 678, 4 sp. 

 adult.— 679, 3 do. shewing interior.— 680, 4 sp. difierent ages, 

 with the 'ear,' 'wing' or 'taU' very much shortened; the 

 larger with Discopora?a 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. 



1 



