354 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
Lepidopleurus halistreptus, Dat. 
Lepidopleurus halistreptus Dall, Proc. U. S. N. Mus., 1902, 24, p. 556. 
U.S. 8. “Albatross,” station 3415, off Acapulco, Mexico, im 1879 fathoms, 
ooze, bottom temperature 36° F. U.S. N. Mus. 109,032; station 3417, in 493 
fathoms, mud, temperature 40°; and station 3418, in 660 fathoms, mud, tem- 
perature 39°. 
The specimen from deepest water, the type of the species, has the valves wider 
in a fore-and-aft direction and more distinctly mucronate 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 4.3,. 
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 angular 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 Da tt, n. sp. 
Animal elongate, with a rather high subangular dorsum, a dirty-white colora- 
tion, and a narrow girdle closely set with very minute spinules, but with no mar- 
ginal fringe of spines; the 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 otherwise uniform over the whole exterior of the 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, 
semilunate, simple; penultimate plate on the jugum 7.2 mm. long; base 10 mm.; 
alt. 6.0 mm. 
U.S. 8. “ Albatross,” station 4647, 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, hard 
bottom, temperature 36°.4 F. 
This species is perhaps nearest to Z. mesogonus Dall, from the Pacific Ocean, 
west of the Queen Charlotte Islands, in 1588 fathoms; that species is, however, 
