OF MOLLUSCA. 205 



Tentacles none ? Eyes lateral. Teeth in three longitudinal series ; 

 central broad, dentate; lateral conical, versatile? Vent centrally 

 posterior, beneath the edge of the mantle, and accompanied by a few 

 slightly pinnate branchiae. Generative organs on right side. " Ex- 

 ternal appearance of Pelta." — Quatrefages. 



1. Runcina. 

 Body elongate, smooth, depressed. Mantle oblong, rounded, 

 covering the head in front, as broad as, and parallel with, the foot 

 on the sides, rather shorter than the foot, and slightly produced and 

 recurved behind. Gill formed of three small plumes, placed under 

 the hinder part of the cloak a little to the right of a central tubular 

 anus. Mouth beneath the mantle, linear, T-shaped, covered with 

 spines. Eyes two, on the sides of the front of the mantle. Organs 

 of generation on the right side. Tongue strap-shaped. " Gizzard a 

 little behind the tongue, consisting of four portions, each bearing six 

 denticulated teeth."— Alder, t. 4. f. 6. Foot elongate, truncated, 

 rounded on the sides in front, rather produced, and tapering 

 behind. 



1. R. Hancocki, Forbes $■ Hartley, B.M. t. C.C.C. f. 2. Lima- 

 pontia, Ann. fy Mag. Nat. Hist, xviii. 289. t. 4. 



Lingual membrane of Runcina Hancocki _. , 



white broad Teeth 1 • 1 • 1 ?, transparent ; ** ^H^H.^ 

 central broad, transverse ; apex recurved, 

 with a broad, three-toothed denticle on each 

 side the middle line ; lateral conical, broad at 

 the base, acute, and curved at the tip ; pre- 

 hensile collar large, rugose, with roundish- 

 tipped tubercles (fig. 114). 



Mantle of Runcina Hancocki separated 

 from the foot by a very distinct groove, truncated in front, raised on 

 each side of the front, and paler edged ; hinder end rounded, pale 

 at the tip. Gills laminar ; leaves rounded, subimbricate, on the right 

 side of the hinder part of the mantle-groove. Foot pale, distinct, 

 simple-edged, pale beneath. On bleached Laurentise in shallow 

 water, "Weymouth. 



Mantle rather coriaceous, the front portion containing the eyes, 

 and separated from the hinder portion of the mantle by a paler band, 

 regarded as the frontal disk of the Bullidce ? 



Order IV. Gymnojbranchiata. 



Gill exposed or contractile into cavities on the surface of the 

 mantle. Adult animal without any shell. Larva shell-bearing, 

 furnished with deciduous cephalic fins. Animal hermaphrodite, 

 with reciprocal impregnation. 



