MORSE: OBSERVATIONS ON LAMELLIBRANCHS. 
187 
papillae as shown in Fig. 40, a. Toward the anterior margin, 
even nearly to the beaks of the shell, are papillae becoming smaller 
though all are bifurcated. The syphons are closely united, no 
line showing their division. They are over half the length of 
the shell and turn slightly upward. They occupy the entin; end 
of the shell even dorsally. The opening of the branchial syphon 
is fringed with long, simple papillae, incurved and distinctly 
alternating with very short papillae, as shown in the enlarged 
drawing of the openings. The anal opening is encircled by a 
ring of a few long papillae with a sUght tinge of brown at their 
Fig. 40. — Machaera costata Gould. 
bases. The valve is large in diameter but extends only a short 
distance bej^ond the papillae. It is mottled with white spots as 
in Solen. In the young shell, 6 millimeters in length, the midrib 
of the shell distinctly borders the posterior outline of the anterior 
adductor muscle. The syphons at this stage are short and the 
papillae are long and few in number. The branchial papillae 
are long and short, alternating as in the adult (Fig. 40, b). They 
have a curious metallic lustre. The protoconch is nearly circular 
and in the successive lines of growth the shell extends posteriorly 
(Fig. 40, c). The mantle is closed except for the pedal opening. 
The creature is verj' timid. 
MACTRA SOLIDISSIMA DiUwyn. 
Fig. 41. Length, 95 mm. 
The foot is longer than the length of the shell, lanceolate, 
with a distinct lateral line. It moves with great vigor, turning 
