242 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 2 



open, the edge of the shell slightly overlapping the vertical walls on the 

 last vi^horl; aperture oval, the posterior angle falling just below the 

 peripheral keel, leaving it exposed on the later part of the body whorl, 

 outer lip thin; inner lip short, sharply curved, with a thin callus over 

 the body of the shell. The type measures: greater diameter, 3.1 mm; 

 height, 0.8 mm. 



Holotype: No. 714 (Calif. Acad. Sci. Paleo. Tj^pe Coll.), from 

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

 Panama. L. G. Hertlein collector. A second but much smaller speci- 

 men was dredged at Bahia Honda, Panama. 



The upper surface of this shell is very similar to that of Cir cuius 

 diomedeae Bartsch*^^ also dredged in Panama Bay, but the finely ser- 

 rated peripheral keel and sharply angled edge to the umbilicus are quite 

 different. A little greater development of the incremental lines would 

 form axial riblets and place the species in the genus Cyclostrema. The 

 umbilical characters of this species are quite distinct. Bartsch describes 

 a genus Scissilabra^^^ type 5. dalli Bartsch, which has a veiy similar 

 umbilicus but the genus is based principally on a notched outer lip, a 

 character not apparent in the present species. 



This species is named for Mr. John L. Nicholson, whose work of 

 arranging the collection of land snails of the California Academy of 

 Sciences has been very helpful in facilitating work on that group of 

 mollusks. 



Delphinoidea hannai Strong & Hertlein, new species 



Plate 22, Figs. 5, 6, 7 



Shell minute, depressed, semitransparent; nuclear whorls 2^, 

 smooth, well rounded ; postnuclear whorls 2, rounded, sutures appressed ; 

 sculpture consisting of fine, close-set spiral threads which are rendered 

 slightly granular by microscopic lines of growth and extend uniformly 

 over the spire and base; of these spiral threads 10 appear on the first 

 whorl between the sutures and about 30 on the last whorl; periphery 

 well rounded ; base rounding into the umbilicus, which in the young 

 stages is open but in the adult shell nearly or quite closed over by an 

 expansion of the body whorl back of the base of the inner lip. Aperture 



^^ Circulus diomedeae Bartsch, Proc. U. S. Nat. Mus., vol. 39, January 9, 

 1911, p. 232, pi. 40, figs. 1, 2, 3. Dredged "in 62 fathoms, on gray sand and 

 broken shell bottom; bottom temperature 59.6°; in the Bay of Panama." 



^^ Sctssilahra Bartsch, Proc. U. S. Nat. Mus., vol. 32, February 8, 1907, p. 

 175. "Type.—Scissilahra dalli." 



