PLEUROTOMARIIDiE. 321 



of the 3^oung shell is converted into a foramen in the adult ; it 

 does not commence until the animal is half-grown. 



S. striatula, Ph., is a littoral species, whilst all the species of 

 Scissurella inhabit deep water. 



Scissurella and Schismope are the analogues respectively to 

 Pleurotomaria and Trochotoma, differing only in size ; hut in the 

 two former genera the shell is translucent, not nacreous, as in 

 the two latter. 



Scissurella, d'Orbigny. 



Etym. — Diminutive of scissus, slit. 



Syn. — Anatomus, Montfort. 



Distr. — Europe, 5 living, 4 tertiary species. S. Bertheloti, 

 Webb (Ixxxii, 92). 



Shell minute, thin, not pearly; body-whorl large ; spire small; 

 surface striated ; aperture rounded, with a slit in the margin of 

 the outer lip ; operculate. The young have no slit. 



Animal like Margarita; tentacles long, pectinated, with the 

 eyes at their base ; foot with two pointed lappets and two long, 

 slender pectinated cirri on each side. Operculum ovate, very 

 thin, with an obscure subspiral nucleus. 



No part of the animal is external to the shell. A living 

 example occurred at Hammerfest, in 40-80 fathoms of water ; 

 when placed in a glass of sea-water it crawled up the side and 

 scraped the glass wath its tongue. It was pale and translucent 

 when living, but turned inky black after immersion in alcohol. 



scHizoTROCHus, Monterosato. Operculum very thin ; shell 

 trochoidal. S. crispata (Ixxxii, 93). 



Seguenzia, Jeffreys. 



Dist7\ — 4 sp. Azores, W. Indies, Pernambuco. 718-1000 fms. 

 ;S. ybrmosa, Jeffreys (Ixxxii, 94). 



Shell globular or conical, glossy, without epidermis, exqui- 

 sitely sculptured ; upper part of the last whorl deeply and widely 

 grooved ; pillar abruptly notched below, and exhibiting a small 

 tooth-like process ; base either deeply umbilicated or imper- 

 forate. 



Differs from the other genera by having a broad sutural slit, 

 instead of on the periphery. Operculum very thin, paucispiral. 



Basilissa, Watson. 



Diatr T sp. Pacific, W. Indies, Canaries, off La Plata, etc., 



at considerable depths. B. lampra^ Watson. 



Shell conical, carinate, umbilicate, pearlj^, last whorl sinuate 

 above ; columella straight, thin, excavated above, angulate but 

 scarcely dentate below ; aperture rhomboidal, the margin not 

 continuous nor joined by palatal callus. 



The sinus is wide, open, shallow, not deep-cleft as in Seguenzia, 



