SCISSURELLA. 57 



very strongly concavely scored. This ridge lies between the suture 

 and the periphery, rather nearer the latter, and forms a crest to the 

 whorls. Above this ridge the slightly depressed surface is scored 

 with very fine threads, parted by little rounded furrows of about 

 twice their breadth ; below the canal edge these spiral threads are 

 stronger, and give a serrated crest to the longitudinal riblets. Spire 

 scalar, but very depressed, the square steps of the whorl edges being 

 very short. Apex small, forming a flat, square-edged coronet, with a 

 slightly depressed minute tip. Whorls 3* to 4, flat or slightly 

 concave above, highly and squarely keeled by the canal-edge, below 

 which they are very slightly constricted ; after this they are tumid 

 to the periphery and on the base. Suture angularly impressed. 

 Mouth narrowly oval, very oblique, largish. Outer lip descending 

 and inflected above, very regularly curved, deeply cut by the fissure, 

 slightly patulous toward the lower outer corner. Inner lip very 

 shortly and thinly appressed on the body between the periphery and 

 the edge of the wide open pervious umbilicus. On the pillar it is 

 barely expanded, is very thin, and runs straight but very obliquely 

 to the point of the base. ( Watson.') Alt. '048 in., diam. '065. 



This is one of the most beautiful species of this very beautiful 

 genus. Its sculpture and form are very marked. ( Watson.) 



Tahiti Harbor, near the reefs, in 20 fms. 



Seissurella coronata WATSON, Challenger Rep., Gasterop., p. 114, 

 t. 8, f. 4, 1886. 



S. DECLINANS Watson. PL 58, figs. 6, 7, 8. 



Shell square above and tumid below, very delicately, sharply 

 sculptured, with a short scalar spire, a minute tabulated apex, an 

 angulated suture, descending mouth, and a large shallow funnel- 

 shaped carinated umbilicus. Sculpture : On the last whorl there are 

 very fine, sharp, close-set, curved radiating threads, which on the 

 upper whorls are strong riblets ; between them the whole surface is 

 finely, closely, microscopically scored with hair-like lines of growth. 

 Spirals the whole shell is delicately marked with very fine, regular, 

 rather distant threadlets ; a little way below the suture and within 

 the periphery is a sharp, narrow keel formed by the upstanding 

 edges of the old canal-ridge. Color dull hyaline. Spire slightly 

 raised, and scalar in very short angular steps. Apex extremely 

 small, tabulated. Whorls 4, of very rapid increase, almost perfectly 

 flat above, keeled by the canal-ridge, below this slightly constricted 

 and then tumid. Suture obtuse angled. Mouth round, small, not 



