MAZATLAN BIVALVES 141 



This species, belonging to the group of B. barbata, setigera, 

 &c., appears peculiar in the structure of the epidermal lamellse, 

 in which are imbedded the rather strong hairs that run down 

 each of the faint radiating grooves, presenting an appearance 

 like a bat's wing, or the whalebones of an umbrella. At 

 regular intervals over the surface is a row of larger hairs ; 

 those on the posterior part are long and stiff, curling round 

 almost into a tube. Only one specimen was found in the 

 boxes : a very few others obtained from a shop were probably 

 from the same collection. Long. '76, lat. 1*3, alt. "57. 

 Sab. Mazatlan ; extremely rare ; L'pool Col. 



Tablet 651 contains the specimen. 



193. BYSSOAECA ILLOTA, Sow. 



Proc. Zool. Soc. 1833, p. 18. 



Area illota, Eve. Condi. Ic. pi. 12, f. 78 Hani. Rec. Shells, 



pi. 18, f. 41. 

 Compare A. Tabogensis, C. H. Ad. Pan. Shells, p. 262, no, 424. 



Shell, as usual, varying in form and markings ; but generally 

 with extremely fine sharp radiating ribs, and fainter concentric 

 ones decussating on a smooth surface ; the ribs being nodulous 

 at the sides, and in the adult on the whole surface, when they 

 become much larger. Epidermis as in B. Tabogensis, between 

 pilose and lamellar, except on the ligamental area, where it is 

 smooth and shining. Shape generally of the B. lactea type, 

 but with very close umbos, inequilateral, and flattened at the 

 ventral margin. Sometimes this is considerably incurved. 

 Hinge teeth few, rather small, in two unequal, slightly curved 

 branches. Ligament solid, adhering only at the posterior part, 

 whence it makes a fine curl round the umbos. A few large 

 specimens were obtained from shops (probably from this col- 

 lection) but only three small ones from the boxes. A rounded 

 specimen measures long. '64, lat. *9, alt. "55. 



A produced sp. *7, ,, 1*2, ,, '58. 



Hob. Gulf of Nicoya, under stones, Cuming. Do. Hinds, 



B. M. Mazatlan ; extremely rare ; L'pool Col. 



Tablet 652 contains a small pair from Mazatlan; and a large 

 valve from a shop. 



L 194. BYSSOAECA GEADATA, Brod. fy Sow. 



Area gradata, Zool Journ. vol. iv. p. 365. Gray in Zool. 

 Seech. Voy p. 152, pi. 43, f. 1. Eve. Conch. Ic. pi. 14, f. 92. 



