220 PACIFIC SCIENCE, Vol. XX, April 1 966 
FIGS. 10-13. Truncatella mariannarum. 10, 11, and 12, sculpture is shown on body whorl only. 13, Trun- 
catella mariannarum, operculum. 
Operculum (Fig. 13) with external calcare- 
ous plate of moderate thickness, showing vague 
arcuate-radiate grooving which is more evident 
toward the periphery. The calcareous plate has 
a waxy texture. It does not extend to the edge 
of the operculum. 
This species is about the same size and shape 
as T. guerinii A and J.B. Villa 1841, which I 
have collected on Manus (Admiralty Islands) 
and Peleliu (Palau Islands). The major dif- 
ference seems to be that T. guerinii has larger 
costae, which are more sharply defined than in 
T. mariannarum Q. and M. 1894. The two spe- 
cies seem readily separable, with no interme- 
diate forms in the several lots which I have 
examined. Yet their similarity suggests that they 
are closely related, and that they may be only 
subspecifically distinct, or perhaps even pheno- 
typic variations of one species. T. guerinii is 
widely distributed in the Indo-Pacific area, as 
Solem (1959:197) has noted. 
Family ASSIMINEIDAE 
Assiminea nitida Pease 
The few specimens of this species were all 
sent to Dr. Cooke. Garrett (1884) gave an ex- 
tensive synonymy of A. nitida, and noted that 
it is generally distributed throughout southern 
Polynesia. Abbott ( 1949) has figured a cotype 
of this species and given a description (Ab- 
bott, 1958), as well as described several new 
subspecies. As he noted, it is likely that this has 
its wide distribution, now known to be from 
east Africa to the eastern Pacific, owing to the 
agency of "man and birds.” 
Family omphalotropidae 
Omphalotropis granum Pfeiffer 
Hydrocena granum Pfeiffer 1854, Proc. Zool. 
Soc. London, p. 307. Not figured. Type locality: 
Isle of Pines, Australian Sea. 
Omphalotropis suhmaritima Quadras and 
Mollendorff 1894, Nachr. d.d. Malak. Ges., p. 
33. Not figured. Type locality: Mariana Islands. 
Two specimens of this species were found 
among the remaining lot of O. fragilis after I 
had divided the material with Dr. Cooke. This 
may be what he designated merely as Omphalo- 
tropis sp., from unsorted material which I sent 
him. The above synonymy is proposed tenta- 
