32-i BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 



Trivia panamensis Dall. 



Plate 12, figures 7, 9, 12. 

 Trivia panamensis Dall, Nautilus, Aug., 1902, 16, p. 43. 

 Dredged in Panama Bay with T. atomaria. U. S. X. Mus. 109,203. 



ERATO Risso. 

 Erato oligostata Dall. 



Plate 11, figure 8. 

 Erato oligostata Dall, Nautilus, Aug., 1902, 16, p. 44. 



TLis is one of tlie smallest, if not actually the very smallest, of the genus. 

 It was dredged in Panama Bay in 1888, with the two preceding species. U. S. N. 

 Mus. 109,207. 



Trichotropidae. 

 CERITIIIODERilIA Conrad. 



Cerithioderma Conrad, Jnurn. Acad. Nat. Sci. Phila., March, 1860, 2d ser., 4, p. 295; 



type, C. prima Courad, op. cit., pi. 47, fig. 30 ; Dall, Trans. Wagner Inst., 



1892, 3, p. 293 ; Harris, Bull. Amer. Pal., 1895, 1, p. 15, pi. 1, fig. 10. Eocene 



of Alabama. 

 Mesostoma Desliayes, An. s. Vert. has. Paris, 1861, 2, p. 416 ; 1st sp. M. pulckra 



Deshayes, op. cit., pi. 28, figs. 13-16. Parisian Eocene. 



Cerithioderma pacifica Dall, n. sp. 



Shell small, thiu, pale olivaceous, with a thin, fibrous, adherent periostracum 

 and about five whorls exclusive of the (lost) nucleus; suture distinct, soincwiiat 

 constricted, not appressed ; whorls well rounded, on tlio fourtii with about sixteen 

 slender low ribs extending vertically from suture to suture, and crossed by two 

 l)rominent spiral ridges of about the same strength as tbe ribs, tlie anterior ridge 

 at the periphery ; on a third similar ridge bordering the base the suture is laid and 

 the ribs cease ; on the base are four spiral ridges, low and rounded, subcqual with 

 subcqual interspaces, but the region of the canal is not sculptured ; in the adult 

 this sculpture is obsolete on the last whorl, and, on the spire, the intersections are 

 sometimes nodulous; aperture wide, ovate, the outer lip tliin, simple, the body 

 with a faint callus; pillar short, twisted, straight; canal represented by a shallow 

 hardly perceptible indentation. Lou. of defective adult, 11 + ; of spire, four whorls, 

 7 ; max. diam. 7 mm. 



