MUCRONELLA VENTRICOSA. 365 



Lepralian ;" found in all the inshore dredgings (Norman, 

 ' Valorous ' dredgings) : Nova Zembla, Jugor-scharr, 10- 

 l4fathoms ; Matotschkin-scharr, 30-50 fathoms ; Kara sea 

 (Stuxberg & Theel) : Bergen (A. M. N.) : on the Falmouth- 

 Lisbon cable, between N. lat. 47° 58' and 47° 35', and in 

 AV. long. 7° 6', from 89-205 fathoms (Sir J. Anderson) . 



Range in Time. Coralline Crag (Searles Wood): Austro- 

 Hungarian Miocene {arreda) (Reuss): Middle Pliocene; 

 Paleolithic (A. Bell) . 



The differences between this species and the preceding 

 are very marked and constant ; nor have I found that they 

 show any tendency to run one into the other. In the first 

 place the cells of M. ventricosa are always very much larger 

 than those of M. Peachii, and the two, which often occur 

 side by side on the same shell, may be distinguished at once 

 by the size alone. They are also much more convex, pre- 

 senting a well rounded anterior surface, and are conse- 

 quently divided by deep sutures. The flat surface, so cha- 

 racteristic of M. Peachii, is never met with in this form. 



The mouth is erect or suberect, and the cell narrows 

 towards it — a peculiarity which is wanting in the last-named. 

 Almost the whole of the inferior margin rises, as it were, 

 into the mucro, which is broad and massive, whereas that 

 of M. Peachii is a central acuminate process, and a much 

 less prominent feature. The spines are not only fewer in 

 number, but different in character from those of the allied 

 species. They are, in the adult, very stout and tusk-like, 

 ranged two on each side, and bend inwards over the aper- 

 ture. The surface is more or less granular, and with a 

 constant tendency to striation, which is not met with at 

 all in the other species. The ooecium is usually very small 

 in proportion to the size of the cell. 



In M. ventricosa the cells are arranged in linear series 



