86 DENTALIUM-GRAPTACME. 



III. An apical slit or notch on convex side only ; not zig-zag 

 clouded. 



a. 17-20 fine sharp ribs, increasing in number, but be- 

 coming faint toward mouth ; puckered elliptically ; a 

 short slit; length 48 mill., 15 times the diam., 



circumcinctum, p. 88. 



a'. Very fine striae near apex, then smooth ; delicate sal- 

 mon tinted ; a deep narrow fissure ; length 31 mill., 

 15 times diam., leptutn, p. 89. 



a". Striae fine, faint in adults ; long and slim, rather 

 straight ; an irregular fissure ; length 38 mill., 12-13 

 times diam., acutissimum, p. 94. 



a'"' Fine stria} on posterior seventh only ; a slight apical 

 notch; length 29 mill., about 11 times diam.; white, 



aciculum, p. 93. 



IV. A slit across the apex ; length 45 mill., about 12 times the 

 diam., splendidum, p. 96. 



V. A slit on the concave side ; striate near apex only ; length 30 

 mill., about 16 times the diam., inversum, p. 95. 



D. SERICATUM Ball. PI. 16, figs. 41, 42, 43, 44, 45, 46 ; pi. 7, fig. 



12. 



Shell considerably curved, rather slender, thin ; very glossy. 

 Subtransparent, bluish-white, with numerous finely zig-zag encircling 

 bands of opaque white, becoming less jagged but still irregular on 

 the larger part of the shell, and generally disappearing toward the 

 aperture. Sculpture of deeply engraved and extremely fine, 

 close, longitudinal stride near the apex (and therefore all over young 

 shells), but soon disappearing, leaving far the greater part of adult 

 shells smooth except for faint annular swellings. Aperture some- 

 what oblique, circular. Anal orifice small, circular, with (in 

 adults) a short slit which is lateral (latero-dorsal to latero-ventral) 

 in position, and sometimes represented by an internal channel only. 



Length 35, diam. of aperture 3'3, of apex 1*1 mill. 



Length 33, diam. of aperture 3'8, of apex 1*2 mill. 



Length 38*5, diam. of aperture 4, length of slit 2 mill. 



Length 37, diam. of aperture 4, length of slit 2'5 mill. 



Length 34, diam. of aperture 3, length of slit 1*2 mill, (imma- 

 ture). 



St. Thomas (Swift) ; St. Martin (Marie) ; Yucatan Strait in 640 

 fms. (Blake). 



