THE NAUTILUS. 137 



up their synonymy. The species of the Pacific coast especially have 

 long been known to be in a very bad state as regards nomenclature, 

 etc. 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 Nautilus, 

 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 

 45*0 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. iii, p. 193, 1867, and erroneously 

 stated to come from Panama. M. lenticularis, Gabb, 18(36, from the 

 Miocene of California is closely related. 

 Mactra Hemphillii n. s. PI. 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, escutcheon marked by prominent 

 elevated radial lines of epidermis ; the dorsal margin pouting in 

 front of the ligament, the posterior slope convex, the posterior flexure 



