PROCEEDINGS OF THE NATIONAL MUSEUM. 293 



Class SCAPHOPODA. 



Order SOLENOCONCHIA. 



Genns DE1STTALIUM Limit?. 



Dentalium megathyris sp. uov. 



Plate ix, Fig. 1. 



Shell remarkably stout and solid, moderately curved ; surface, when 

 not eroded, shilling; color yellowish white, generally with some dark 

 extraneous matter lodged in the grooves of the sculpture; anal end 

 circular, small, simple, with a sharp edge, about 2 mm in diameter; toward 

 this end the shell is more curved than anteriorly ; surface with strong 

 flattened longitudinal threads about l mm from center to center, the 

 interspaces sharply grooved in rather deep square-sided channels; 

 about the middle of the shells the ribs begin to bifurcate so that the 

 anterior sculpture, though of the same character, is some two or three 

 times as fine as the posterior; in old age the sculpture is interrupted 

 around the aperture; transverse sculpture only of fine incremental lines ; 

 oral aperture sharp edged, a lit tie oblique, nearly circular, slightly flat- 

 tened in an anteroposterior sense; interior milk-white; texture of the 

 shell porcellanous with an external chalky stratum under the smooth 

 exterior, which is frequently much eroded even in life; maximum longi- 

 tude of shell, 95; diameter of aperture, 17.5; anteroposterior diameter 

 of same, 15.5 mm . 



Hab.— U. S. Fish Commission Station 2807, near the Galapagos 

 Islands, Pacific Ocean, in 812 fathoms, globigeriua ooze, bottom tem- 

 perature 38°. 4 F.; also off Chiloe Island and southwest Chili at Station 

 2788 and 2,789, in 1,050 and 1,342 fathoms; temperatures 36°.9 and 

 35o.9 F. 



This is one of the finest species of the genus known, and was taken 

 alive in some numbers. The" young recalls D. ceras Watson, but the 

 shell changes in rate of increase and form of longitudinal ribs as it 

 grows. It is a little straighter near the anal end, and the adult is more 

 funnel shaped, with flatter ribs than in D. ceras. 



The radula is short, with the formula ,+n+i. The median tooth is 

 wide, subrectangular, arched a little in front. The laterals on each side 

 have a projecting stout cusp; the uncini are flat rhomboidal plates. 

 The whole radula bears a strong resemblance to that of Entalis strioldta, 

 as figured by G. O. Sars. (Moll. Reg. Arct. Norv., t. I, f. 1, la.-c.) 

 The oesophagus is short; the stomach short and cordate, stuffed with 

 foraminifera. The soft parts, as preserved in alcohol, seem ridiculously 

 small and out of proportion to the massive shell. 



