244 



OlS THE TOrOGRAPHY AlV^D GEOLOGY 



LUCAPINA Gray. ' - ■ ... 



L. altcrnata. Say., sp. 



F. alter nata. Say., Jour. Pliil. AcacL, 1 ser., Vol. IL, p. 224. ' 

 L. altcrnata. H. and A. Ad., Gen. Ecc. IMoU. 



Half a dozen specimens were found, the largest not quite an inch in length. 



DENTALIUM. Linn. 

 D. d i s s i m i 1 e. Guppy, [Quart. Joitr. , Vol. XXII., p. 292, pi. 17, fig. 4. 



I have a shell answering to Guppy's description and figin-e, except that it seems 

 more robust than the latter. 



Another form, probably a variet^^, differs from this in being smooth but with six 

 sharp longitudinal ridges, not, however, like D. liexagonum. In apical angle and 

 curve it agrees Avith the above. , ' 



D. affine. Gabli, n. s. ■ ■ 



Shell rapidly tapering, gently curved, mai'ked by six or eight large rib.s, with a variable number of smaller rib.s 

 interposed. Besides these the shell is sculptured by minute longitudinal lines, crossed by equally small lines of 

 growth, giving the surface a finely woven appearance. Length about 1.5 inch. 



Difl'ers from JJ, dissimile in the amount of curvature and in widening much more 

 rapidly towards the mouth ; also in being scul]3tured over the entire surface. J^Tearest 

 to D. elejihcmtmum, but smaller, less curved, and with finer sculpture. 



The large ribs are not uniform in pattern, sometimes being as few as six, while in 

 other specimens the whole surface is covered with ribs of pretty nearly uniform size. 



I have two specimens which seem to indicate a larger species, in which the loiigi- 

 tndinal ribs are of uniform size ; and while the minute sculpture described above does 

 not occur, it is replaced by the lines of growth being finely squamose. In the absence 

 of more material, I do not feel warranted in naming it. 



D. Haytensis.' Gabb, n, s. 



Shell small, nearly straight, increasing very gradually in size, surface polished. 



This little shell differs from the preceding by its straigliter form and entirely 

 smooth surface, as well as b}^ the nearly parallel sides. 



? D. r u d i s. Gabb, n. s. 



Shell long, straight, slender, massive ; widening very gradually. Surface sculptured by longitudinal ribs, 

 coarse, undulated, and sometimes broken by transverse wrinkles. Length 2.5 inches. 



This shell has the general form of a sti'aight DentaUum, but its thick substance 

 and its rough sculpture seem to indicate a generic difference. Its surface is not 

 unlike that of some species of Ilijij^urite in the style of ornament. 



D. p o n d e r o s u m. Gabb, n. s. 



Shell elongate, slender, very slightly arcuate, the greater curve being at the tip ; surface with a few h>ngitudinal 

 ribs at the apex, which become obsolete as the shell grows older ; beyond these there are no ornaments except the 

 faint lines of growth. Internally the shell is thickened by deposition of shelly layers so as to reduce the internal 

 diameter to a fourth of the external. 



