354 bulletin: museum of comparative zoology. 



Lepidopleurus halistreptus, Dall. 

 Lepidopleurus halistreptus Dall, Proc. U. S. N. Mus., 1902, 24, p. 556. 



U. S. S, "Albatross," station 3415, off Acapulco, Mexico, in 1879 fathoms, 

 ooze, bottom temperature 36° Y. U. S. N. Mus. 109,032 ; station 3417, in 493 

 fathoms, mud, temperature 40° ; and station 3418, in 660 fathoms, mud, tem- 

 perature 39°. 



Tlie specimen from deepest water, the type of the species, has the valves wider 

 in a fore-and-aft direction and more distinctly mucrouate than those from the 

 other two stations. 



The type has the first intermediate valve in front of the tail-valve ■with an axial 

 length of 5.6 mm., a basal width of 10 mm., and an altitude above that base line 

 of 4.5 mm. 



The corresponding measurements from a specimen from station 3417 are 4.5, 

 10.0, and 3.5 mm.; and from station 3318, 3.5, 9.6, and 3.5 mm. It is obvious 

 that the shallow-water specimens have the intermediate valves shorter and less 

 elevated mesially and consequently a less angidar back ; there is also a pair of im- 

 pressed lines which tend to differentiate the jugal from the pleural tracts. The 

 measurements of the tail- valves did not differ like those of the intermediate valves. 

 I was unable to discern any further differences, but, if those above indicated are 

 held to have any systematic weight, the shallow-water specimens might be con- 

 sidered as a variety abbreviatus. 



Lepidopleurus opacus Dall, n. sp. 



Animal elongate, with a rather high subangular dorsum, a dirty-white colora- 

 tion, and a narrow girdle closely set with very minute spiiiules, but with no mar- 

 ginal fringe of spines; tlie jugal is not perceptibly marked off from the pleural 

 areas, and the lateral areas are only indicated by a feeble radial depression some- 

 times hardly visible; the sculpture consists of very minute ovate, flat, close-set 

 granulations, like scales, obscurely arranged radiately with reference to the mucro, 

 but otlierwise uniform over the whole exterior of tiie valves; posterior valve with 

 the jugum slightly arcuate longitudinally, ending in a prominent subcentral mucro ; 

 the posterior area slightly depressed, the sutural plates short, anteriorly directed, 

 with an inclination of 45° laterally; interior white; intermediate valves with a 

 wide sinus, short sutural plates, and an almost obsolete notch ; anterior plate small, 

 semiiunate, simple ; penultimate plate on the jugum 72 mm. long; base 10 mm.; 

 alt. 6 mm. 



U. S. S. "Albatross," station 4G47, between the Galapagos Islands and the 

 Peruvian coast, in 2005 fathoms, ooze, bottom temperature 35°. 4 F. U. S. N. 

 Mus. 110,664. Also at station 3392, Gulf of Panama, in 1270 fathoms, iiard 

 bottom, temperature 30°. 4 F. 



Tiiis species is perhaps nearest to Z. maogonnx Dall, from the Pacific Ocean, 

 west of the Queen Charlotte Islands, in 1588 fathoms; that species is, however, 



