1 76 Dall Diagnoses of New Species of Mollusks. 

 Ischnochiton biarjuatus sp. nov. 



Animal about 18 mm. long and 7 mm. wide (in the dry state); girdle 

 narrow, with very small, close-set, more or less imbricating, brownish 

 scales; valves rounded evenly above, only the lateral areas distinct; an- 

 1 terior valve with 7 or 8, median with 1, posterior valve with 11 slits; in 

 terior of valves rose-pink; exterior ashy, marbled with lilac and brown, 

 an obscure lilac median line on the medial valves; sculpture of undivided 

 central areas formed by two sets of arcuate radiations crossing each 

 other obliquely and with the inter-reticulations impressed or punctate, 

 so that an irregularly zigzag effect is produced by the arrangement of 

 the punctations; lateral areas irregularly concentrically vermiculate, the 

 ' spaces between the elevated ridges deeply minutely punctate, with some- 

 what of a zigzag effect here also; the sculpture of the anterior valve re 

 sembles that of the lateral areas; of the posterior valve the mucro is low, 

 sub-central and inconspicuous, the central area sculptured like that of 

 the medial valves, the posterior area like the anterior valve; the sutural 

 plates are quite short and the sinus smooth and wide. There is no notice 

 able mucro to the medial valves. 



The peculiar sculpture of this species separates it from those already 

 described from this region. In a general way it recalls the very young 

 of /. magdalenensu Hinds. The type is No. 10J.308, U. 8. National 

 Museum. 



