THE NAUTILUS. 137 
up theirsynonymy. The species of the Pacific coast especially have 
long been known to bein a very bad state as regards nomenclature, 
ete. Several long known forms appear, on investigation, to be 
really nameless, the titles belonging to other less conspicuous spe- 
cies having been applied to them, while some of the earliest named 
forms have been lost sight of. I hope to furnish the Nauritus, 
shortly, with synonymic lists of the east and west coast Mactras, 
pending the completion of which the following descriptions are 
offered. 
Mactra catilliformis Conrad. PI. V, fig. 3. 
Shell large, thin, whitish or straw color, irregularly concentric- 
ally striated, with a gray, wrinkled epidermis, inflated short-oval 
subequilateral valves and closely adjacent inconspicuous beaks ; 
anterior end of shell evenly rounded in front, a little shorter than 
the posterior end; lunule narrow, impressed, escutcheon narrow, 
longer, rather obscure; posterior end of valves rounded, slightly 
compressed and with a narrow gape when closed; hinge resembling 
that of M. polynyma Stm., but more concentrated, cartilage pit 
large, rather produced; posterior muscular impression larger, pall- 
ial sinus rather large, rounded in front. There is a faint posterior 
flexure of the valves and a feebly marked area above it, on which 
the epidermis is more conspicuous. Lon. 108-0, alt. 87-0, diameter 
450 mm., in a moderately sized pair, but the adult reaches 140-0 
mm. in length. 
Distribution: Neeah Bay to San Diego, Cala. 
This is Standella californica Carpenter, but not of Conrad or 
Deshayes. It was imperfectly described without a figure by Conrad 
in the Am. Journ. Conch. vol. ili, p. 193, 1867, and erroneously 
stated to come from Panama. J. lenticularis, Gabb, 1866, from the 
Miocene of California is closely related. 
Mactra Hemphilliin.s. Pl. V, fig. 2. 
Shell large, thin, inflated, subequilateral, creamy white with a yel- 
low thin epidermis, which over the body of the shell in young shells 
is beautifully evenly concentrically striated and on the posterior 
dorsal area is irregularly wrinkled, with an elevated raphe of epider- 
mis at the margin of the area; beaks rather prominent, the ante- 
rior end of the valves longer than the posterior; posterior dorsal 
slope excavated; lunule obscure, escutcheow marked by prominent 
elevated radial lines of epidermis; the dorsal margin pouting in 
front of the ligament, the posterior slope convex, the posterior flexure 
