DENTALIUM-COMPRESSIDENS. 125 



The strong compression from concave to convex sides is a very con- 

 spicuous feature of the species. In a section of the tube the arc 

 along the concave side is much less curved than the other. The pe- 

 culiar "texture of the shell which thus seems to be built up of 

 minute, square-faced rods laid side by side," as Watson describes it, 

 is not noticeable in the specimens before us. 



The calibre of the tube increases more rapidly than in the closely 

 allied D. ophiodon Dall, and it is more compressed. 



D. BREVICORNU Sharp & Pilsbry, n. sp. PI. 22, figs. 53, 54, 55. 



Shell small, moderately curved, strongly compressed between the 

 convex and concave faces, rapidly tapering, thin, buff-white. Sculp- 

 ture: rather inconspicuous growth-lines and wrinkles, and exces- 

 sively shallow, hardly noticeable traces of longitudinal depressions 

 scarcely to be called sulci. Aperture not oblique, irregularly ovate, 

 the outer margin rounded, inner much flattened. Apex not very 

 small, its orifice rounded-oval. Length 9'5, transverse diam. of 

 aperture 2*2, diam. from convex to concave sides 1*7 mill., greatest 

 diam. at apex 0'7 mill. 



Near Galapagos Is., 634 and 812 fms., bottom temp. 40 ; off 

 Mazatlan, 995 fms. (U. S. Fish Commission). 



Very closely allied to the Antillean D. pressum Sharp & Pils., 

 but the tube increases more rapidly in calibre and is decidedly less 

 compressed on the outer curve. Type is No. 122809, U. S. Nat. 

 Mus., from the locality first mentioned above. 

 D. SIMPLEX Pilsbry & Sharp, n. sp. PI. 27, figs. 88, 89. 



Shell short, decidedly curved, the bend mainly in the posterior 

 half, very rapidly enlarging, tapering regularly from the large apert- 

 ure to the apex; thin, bluish-white, a little translucent, more or less 

 flecked with opaque white (by incipient surface decay), or with 

 eroded spots. Glossy, with close, fine, distinct growth-striae, very 

 obliquely passing around the tube, bending backward on the convex, 

 forward on the concave side ; in most specimens also showing faint, 

 low traces of longitudinal cords on the convex side. Aperture some- 

 what wider than long, quite oblique, the peristome thin. Anal 

 orifice circular, simple when perfect, but often with irregular, broken 

 edge. Length 8*6, diam. at aperture antero-posteriorly 1 *75, laterally 

 1*9 mill.; diam at apex 0'7 mill. 



Off Tillamook Harbor, Oregon, in 786 fras. (U. S. Fish Commis- 

 sion). 



