NO. 12 STRONG AND HERTLEIN : MARINE MOLLUSKS 229 



by a rounded cord below which the suture is laid, leaving it fully ex- 

 posed above the suture on the spire; base short, with a broad, rounded 

 spiral cord bounding the wide umbilicus; aperture oval, oblique, outer 

 lip moderately thick; inner lip entirely separated from the body whorl 

 but fusing with the lower portion of the columella and connected with 

 the posterior angle of the outer lip by a shelly bridge ; columella strong, 

 curved. The type measures: length, 1.1 mm; diameter, 0.7 mm. 



Holotype: No. 706 (Calif. Acad. Sci. Paleo. Type Coll.), from 

 Loc. 27,229 (C.A.S.), dredged in from 3 to 9 fms. in Bahia Honda, 

 Panama. L. G. Hertlein collector. One hundred thirty additional speci- 

 mens were dredged at the same locality. 



This exclusively west coast genus of shells has not previously been 

 reported south of Magdalena Bay, Lower California, from which lo- 

 cality Amphithalatnus stephensae Bartsch^^ has been recorded. The pres- 

 ent species is quite similar to Amphithalamiis inclusus Carpenter,^^ de- 

 scribed from San Diego, California. It differs principally in the slightly 

 smaller size and in having the peripheral cord fully exposed on the spire. 



This species is named for Mr. Henry Trost of the M. H. de Young 

 Museum, in Golden Gate Park, San Francisco, California. 



Rissoina adamsi Bartsch ?var. 



Plate 19, Fig. 4 



Rissoina admnsi Bartsch, Proc. U. S. Nat. Mus., vol. 49, 1915, pp. 47- 

 48, pi. 30, fig. 5. "The type, which is in the Amherst collection, 

 comes from Panama." 



Hypotype: No. 740 (Calif. Acad. Sci. Paleo. Type Coll.), from 

 Loc. 27,228 (C.A.S.), dredged in from 3 to 9 fms. off Taboga Island, 

 Panama. L. G. Hertlein collector. Forty specimens were dredged off 

 Taboga Island, Panama, and 25 were dredged in Bahia Honda, 

 Panama. 



Adams described Rissoa janus^'^ from 2 specimens found in the sand, 



^^ Amphithalamus stephensae Bartsch, Proc. Nat. Mus., vol. 70, art. 11, 

 April 8, 1927, p. 28, pi. 4, fig. 5. "Collected by Mrs. C. L. Simons in Magdalena 

 Bay, Lower California." Other specimens collected at Turtle Bay, Lower Cali- 

 fornia. 



56 Amphithalamus inclusus Carpenter, Ann. and Mag. Nat. Hist., ser. 3, 

 vol. IS, 1865, p. 181. "Hab. Sta. Barbara (Jewett) ; S. Diego (Cooper)."— 

 Bartsch, Proc. U. S. Nat. Mus., vol. 41, 1912, p. 264, text fig. 2. San Diego, 

 California; Santa Catalina Island, California. 



57 Rissoa janus C. B. Adams, Ann. Lyceum Nat. Hist. New York, vol. 5, 

 1852, pp. 403, 538. "Panama." 



