258 University of California Publications in Zoology | Vou. 14 
the middle for the passage of the byssus; hinge margin straight, and ascending 
for about two-thirds the length of the shell so as to give it additional height, 
then, by a regular downward curve, it produces an obliquely rounded termi- 
nation to the shell; a broad, elevated ridge crosses obliquely from the beaks to 
this termination, above which the shell is compressed; surface ornamented 
with numerous radiating, somewhat undulating, occasionally branching ribs, 
most conspicuous above and behind, very fine on the anterior third. Shell 
silvery-white, the muscular impressions and margins of a livid color; margin 
of the posterior half and anterior side crenulated by the ribs.’’ 
This exotic species was first reported from a point ‘‘three miles 
north of Stanford University’’ by Stearns in 1899. Although it was 
not taken by the Survey, it is reported to occur within the lower 
division of the bay in sufficient numbers to be marketed occasionally. 
On the Atlantic coast, Sumner et al. (1911) report this species as being 
abundant along marshes and sandy shores. 
Range-—Known on the Pacifie Coast only from San Francisco. 
Modiolus rectus Conrad 
Modiola recta Conrad (1837), p. 243, pl. 19, fig. 1; Carpenter (1863), 
p- 643. 
Modiolus rectus, Arnold, R. (1903), p. 120. 
DescriptionThis species was originally described by Conrad (1837) as 
follows: 
‘‘Shell produced, smooth, thin, anterior margin elevated; posterior side 
cuneiform; color brown, with a broad pale strip extending from the beak to- 
wards the posterior margin; within very glossy and iridescent.’’ 
Occurrence.—At station D 5723* (f.) and questionably at D 5723 
(8), D 5788 (8), D 5828 B (1). 
A fragment of a shell that was determined by Dall as belonging 
to this species was dredged by the Survey in the northern portion of 
the lower division of the bay. Several small living specimens have 
been referred to this species. 
Range—Puget Sound to Magdalena Bay, Lower California. 
Modiolus politus Verrill and Smith 
Modiola polita Verrill and Smith (1880), p. 400. 
Description—This species was originally described as follows: 
‘<Shell thin, translucent, without sculpture; epidermis pale yellow, smooth 
and polished. Umbos prominent; hinge-line straight; posterior end broadly 
rounded, compressed; anterior end prolonged decidedly beyond the beak, narrow, 
rounded. Greatest length, 40; breadth, 21 mm.’’ 
Length, 6 to 7 mm. 
Occurrence-—At stations D 5788 (1), D5789 (1), and question- 
ably at D 5821. 
