246 University of California Publications in Zoology | Vou. 14 
PELECYPODA 
NUCULACEA 
NUCULIDAE 
Nucula Lamarck 
Nucula tenuis (Montagu) 
Plate 14, figure 4 
Arca tenuis Montagu (1808), pl. 29, fig. 1. 
Nucula tenuis, Gould (1841), p. 155. 
Description.—This species was originally described as follows: 
“Shell sub-cordate, smooth, white, covered with an olivaceous epidermis: 
umbo very small: beaks slightly inflected, and placed near to one end. Inside 
smooth, white, and somewhat nacred; margin thin and entire: hinge pectinated 
with about fifteen elevated teeth placed within the margin, six on one side and 
nine on the other, divided by a small concave plate that projects inward. 
Greatest diameter a quarter of an inch; the length not quite so much.’’ 
Length, 4 to 8 mm. 
Occurrence—At stations D 5787 (9), D5786* (2), and D5788 
(Gl, 
This mollusk was dredged by the Survey in the vicinity of the 
Farallon Islands, at a depth ranging between 39 and 68 fathoms from 
a bottom comprised of dark greenish sand. 
Range.—Cireumpolar. Arctic Sea to Coronado Island, California 
(Dall). 
Acila Adams 
Acila castrensis (Hinds) 
Plate 14, figures 1 and 2 
Nucula castrensis Hinds (1843b), p. 98. 
Acila castrensis, Carpenter (1863), p. 664; Gabb (1869), p. 102; Arnold, R. 
(1903), p. 95. 
Description—This species was described by Arnold, R. (1903), as follows: 
“«Shell small, trigonal, convex, of medium thickness; umbones posterior to 
the center, turned posteriorly; anterior end longer than posterior, rounded; 
posterior end short, truncated; surface divaricately sculptured; hinge with 
prominent internal cartilage-pit and numerous sharp teeth on each side.’’ 
Length, 4 to 11 mm. 
Occurrence.—At stations D 5785 (1,1), D 5788* (15), D 5789* (3). 
As far as is known this species has not hitherto been reported from 
this region. It is restricted to the collections from the open ocean. 
Living specimens were dredged off San Francisco by the Survey at 
*Specimens for stations thus designated were determined by Dall. 
