MORSE: OBSERVATIONS ON LAMELLIBRANCHS. 191 
posterior region behind the beaks is much the shorter. The 
posterior slope from the beaks is abrupt and from the lower 
half of this slope the syphons protrude. These are separated, 
short, the anal being larger in diameter than the branchial and 
the branchial nearly twice as long as the anal. The anal syphon 
is broad-shouldered at its base dorsally and is covered with 
short truncated papillae. The opening may be circular or 
sinuous. Within, silver}' encircling ridges are seen (Fig. 43, a 
and b). The valve is extremely short and as wide as the opening 
from which it springs (Fig. 43, c). The papillae of the branchial 
syphon are long and short and are roughly arranged like the 
tentacles of an actinoid polyp with six large papillae, six inter- 
mediate papillae, and smaller ones between these and the primary 
ones (Fig. 43, d). These papillae are pointed but the syphon, 
like the anal syphon, is covered with short, blunt papillae. The 
foot is large, keeled, and pointed. The pedal opening is long 
and fringed with short papillae, and even when the mantle is 
closed the line of junction is marked (Fig. 43, e). The animal 
is light yellowish in color and the epidermis covering the shell 
is distinctly iridescent. 
MYA ARENARIA Linn6. 
Fig. 44. Length, 70 mm. 
The syphonal tubes are united, the branchial twice the diameter 
of the anal. When fully extended they exceed twice the length 
of the shell. Papillae of various lengths fringe the opening of 
the branchial syphon; these are flattened radially and a few are 
bifurcated. They are light brown or nearly white in color. At 
the base of or between the papillae the darkest brown, nearly 
black color is seen; immediately below, a ring of small papillae 
encircles the tube. These are all recurved. The valve is short 
and broad with large opening nearly as wide as the base of the 
tube, light brown in color. Surrounding the valve is a row of 
papillae of varying lengths. The appearance of the syphonal 
openings varies in different individuals; in some the papillae are 
nearly absent, probably bitten off by some fish. Viewed from 
the end, the branchial tube appears circular, the anal tube in 
section looped to it. In some, the partitions separating the tubes 
appear like a straight wall. In young specimens the papillae are 
