MOLLUSCA OF THE ' CHALLENGER ' EXPEDITION. 101 



its upper corner, and a small and very transverse rift at the 

 pillar. Outer lip sharp, thin, straight, perpendicular, angulated 

 at the basal corner, flat across the base, turned in towards the 

 mouth and pinched in at the pillar, where it joins the pillar-lip, 

 closing in the side of the small siphonal canal, whose edge 

 is sharp and straight, or a very little contracted all round. Pillar 

 straight in front, then very much bent back, so that its posterior 

 line almost stands on the edge of the base. JPillar-lip expanded 

 but abruptly defined on the base, blunt but projecting on the pillar, 

 where it is covered by and cemented to the outer lip. H. 0*22. 



B. 0'07 5 least 0*06. Penultimate whorl O032. Mouth, length 

 0037, breadth 0'035. 



This beautiful little species is very like in general aspect to 



C. perversum, L. ; but, apart from other obvious differences, the 

 sculpture of the apex is quite distinct. In that species the 

 extreme apex has about seven spiral scatches, parted by rough- 

 ened threads, and the following whorls are beset with much closer- 

 set and more numerous riblets, and they have two close-set 

 spirals at the carina. The whole of this sculptured apex (in 

 C. perversum) is stumpier, and the whorls are not so angulated, 

 and the extreme point is blunter. 



T. Hindsii, Desh. (Bourbon Moll. p. 99), is very near, but is 

 less contracted in front towards the base, has not there near the 

 mouth four rows of pearls, has the pearls white on a brown ground, 

 has not the single amber thread, and is a little narrower in 

 proportion. 



2. Cerithittm (Thiforjs) bigemma, n. sp. 



St. 24. Mar. 25, 1873. Lat. 18° 38' 30" N., long. 65° 5' 30" W. 

 St. Thomas, N. of Culebra Island, Danish "West Indies. 390 fms. 

 Coral-mud. 



Shell. — Sharply conical, high and narrow, solid, opaque, brilliant, 

 yellowish white. Sculpture. Longitudinals — the whorls are crossed 

 by rows of tubercles with broad and rounded hollows between ; 

 of these longitudinal rows there are 17 to 18 on the last, and 

 about 14 on a great many of the preceding whorls ; besides these 

 the surface is sharply, distinctly, and pretty closely scored by 

 minute lines of growth. Spirals — a prominent spiral band 

 encircles the whorls formed by two rows of rounded tubercles, 

 which in each row are connected by a spiral thread ; of these 

 threads the lower is rather the larger, sharper, and more pro- 

 minent. The distance between these threads is very nearly 



