Cyclostrema, Adeorhls, Vitrinella, and related genera. 133 



junction with the strongly curved outer-lip and reflected along the 

 umbilical region, but not thickened. Surface appears smooth but 

 under the microscope it is covered, except the nucleus, with delicate, 

 much separated, spiral threads which extend up into the umbilicus. 

 The animal is drawn so far into the shell that the operculum, if 

 present, cannot be seen. 



Greatest width, about 1.5™"" ; height, the same. 



Although at first sight this species strongly resembles a Zissospira, 

 in the large size of its nucleus, regularly increasing whorls, and form 

 of its aperture it approximates to Rissoa (Setia) triangularis Watsoa 

 (Report Voy. Challenger, Zool. Scaphopoda and Gasteropoda, xv, 

 p. 611, pi. xlvi, fig. 2, 1885), but is much smaller with more swollen 

 whorls. 



Subgenus Ganesa Jeffreys, 1865. See page 114. 

 Lissospira (Ganesa) Dalli (Yerrill). 



Cyclostrema trochoides Verrill, Notice of Recent Add. to Mar. Invert., Part ii, Proc. 

 U. S. Nat. Mus., iii, p. 378, 1880, non G. 0. Sars, 1878. 



Cyclostrema BalliYemW, these Trans., v, p. 532, pi. Ivii, fig. 39, 1882; Expl. 

 Albatross, Report U. S. Com. Fish and Fisheries for 1883, p. 569, pi. xxvii, fig. 99, 

 1885. Tryon, Manual of Conchology, x, p. 97, pi. 33, fig 100, 1888. 



Cyclostrema fulgidus Dall, Bull Mus. Comp. Zool., xviii, p. 393, 1889, non {Trochus 

 fulgidus) Jeffreys, 1883. 



Cyclostrema fulgidum Dall, Bull. U. S. Nat. Mus., No. 37, p. 166, pi. Ixiii, fig. 99, 

 1889. 



About a dozen specimens have been recorded as found at five 

 stations between N. lat. 41° 53', W. long. ^5° 35' and N. lat. 38° 

 0]' 15', W. long. 73° 44', in 390-1188 fathoms, 1880-1886. 



Specimens from very deep-water are not of so firm a texture as the 

 typical examples, the entire surface appears chalky without much 

 lustre, and the lines on the base are less distinct. There is little 

 resemblance between G. Dalli and the figure of Trochus fulgidus 

 as given by Mr. Jeffreys, who described that species as having the 

 peritreme "not continuous or complete ;" while Dalli has the peri- 

 treme continuous, attached to the body-whorl for a considerable dis- 

 tance so that the form of the aperture is somewhat modified, and the 

 columellar margin is flattened so that it spreads slightly over the 

 umbilical region. The umbilical chink or fissure appears channeled 

 and is defined by a raised thread, as in other species of Ganesa. 



