228 
MARINE SHELLS OF WEST COAST OF NORTH AMERICA 
with a longitudinal elevation or fold extending from the beak to the front; 
beak short, slightly incurved, and truncated by a large incomplete foramen, 
margined anteriorly by a portion of the umbo of the opposite valve, and 
laterally by two small deltidial plates; beak ridges strongly defined, leaving 
between them and the hinge line a flat or gently concave smooth area. 
Surface of valves either smooth or more or less covered with faint or 
strong angular ribs, here and there bifurcating, or with a short rib interpo¬ 
lated between the larger ones. Shell structure perforated by minute canals. 
In the interior of the dorsal valve the hinge plate is divided; cardinal 
process small, and from under it a mesial septum of small elevation extends 
to about half the length of the valve. Loop long, doubly attached, first 
to the base of the hinge plate, then to the anterior extremity of the mesial 
septum of an oblique lamina given off from about the middle of the length 
of the principal stems of the loop, when, after having attained their 
greatest length, they become reflected in the shape of a loop. Colour 
varying from light ashy yellow to a light or dark livid purple or red 
mixed with yellow, deeper in colour on the lines of growth. Length, 1 
inch, 3 lines; breadth, 1 inch, 7 lines; depth, 10 lines. (Davidson.) 
Type in British Museum. Type locality, Puget Sound, Washington. 
Range. Southeast of Alaska Peninsula, Vancouver Island; Puget 
Sound; Monterey Bay; San Pedro, California. 
Terebratalia transversa caurina Gould, 1850. 
Plate 16, figs. 4, 5, 6, 7. 
Proc. Boston Soc. Nat. Hist., 3:347. Wilkes Expl. Expcd. Shells, p. 468. Am. Jour. 
Conch., 6:119; pi. 6, figs. 1-3, 1870. 
T. parva, fusco-cinerea, transversa, convexiuscula; quincuncialiter 
punctata, costis angulatis ad 12 interdum bifurcatis radiata; margine 
ventrali circulari, flexuoso; apice acuta, rectangulari; lateribus recti- 
linearibus, incumbentibus; rostro bervi, vix curvato; foramine circulari, 
interrupto; apophysis branchialis tenuissima, angustata. Long., *4; lat., 
n / 2 o; alt., % poll. (Gould.) 
Shell small, dusky-ash colour, moderately convex, rather broader than 
long; ventral margin rounded, with a central broad flexure, and cor¬ 
responding depression in the smaller, and angulation of the larger valve; 
surface with twelve or more obtusely angular, radiating ribs, gradually 
enlarging, and sometimes bifurcating; interspaces and elevations about 
equal; the whole with microscopic opaque dots; small valve having the 
apex a little pointed, and the posterior outlines otherwise rectilinear, and 
forming a very obtuse angle; large valve forming about a right angle at 
beak, but with the lateral outline concave, and the margin incumbent, 
forming a broad, nearly flat area; beak but little raised, pointed; the 
ligament aperture very large, circular, a part of its margin formed by the 
