1894. PROCEEDINGS OF THE NATIONAL MUSEUM. 687 



specimeu showing indications of a wide, shallow ventral sinus at the 

 apex; shell little curved, and the sculx^ture shows no rotary tendency. 

 Length of shell, 78; diameter anteriorly, 8.5; posteriorly, 1.3; maximum 

 divergence from a chord connecting the extremities, 8.5 mm. 



Stations 3472 and 3476, in 295 and 298 fathoms. Nos. 107022 and 

 107023, U.S.N.M. 



This shell differs from D. candidum, Jeffreys, by being more cylin- 

 drical and, so far as my present specimens go, without the long, slen- 

 der ventral slit of that species. From D. ceras, Watson, as figured, it 

 is distinguished by being straighter and less sharply sculptured, besides 

 being much larger, but Watson's specimens were young. With a few 

 specimens it is easy to separate species of Doi^a/iMw, but if one has 

 numerous specimens from various kinds of bottom the difiiculty 

 increases greatly. D. solidum', Verrill; D. ceras, Watson, and D. candi- 

 diim, Jeffreys, appear to merge into one another, yet individual speci- 

 mens appear very distinct when one has not a connecting series. The 

 present species, by its somewhat more cylindrical form, seems suffi- 

 ciently distinct to be named, but, with that exception, is very closely 

 related to the grou]) of forms abo \e enumerated. 



All the specimens were dead, discolored, and occupied by annelid 

 tenants. 



Class PELECYPODA. 



Family Euciroid.e. 



Geuus EUCIROA, Dall. 



When first proposed,* this group was sux)posed to be sufficiently 

 distinct from Verticordia as defined in the text-books, but later t a 

 careful study of numerous species of Verticordia, including the type 

 species of that genus, led to the belief that it could at most form a 

 section of the older group, and as such it was included in my final 

 report. | It was only known from separated valves of the type species 

 V. {E.) elegantissima, Dall, dredged in 300-750 fathoms in the Antilles. 

 Since then a related and very elegant species has been dredged in the 

 Indian Ocean by the Investigator, and has been described § by Wood- 

 Mason and Allcock under the name of Verticordia {Euciroa) ehurnea. \\ 



I have now the pleasure of adding a third and very beautiful species 

 from the Pacific, which, being taken with the soft parts intact, ena- 

 bles me to complete my description of the group and establish it as 

 even more than generically separate from the tyi^ical Verticordia. 



* Bull. Mus. Comp. Zool., v, pp. 61, 62, 1878. 



t Op. cit., IX, p. 106, 1881. 



t Op. cit., XII, pp. 196, 291, Sept., 1886. 



§ Ann. Mag. N. H., Dec, 1891, p. 447, fig. 14. 



II Sowerby, overlooking this description and figure, redescribed tliis species under 

 tlie name of V. optima in Proc. Mai. See, Lend., i, p. 39, pi. v, fig. 3, Mar., 1894. 



