4-54 Mr. W. Clark on the Conovulidse, 



membranous, gently reflected at the sides on itself, which reflex- 

 ion it in some measure retains on the march, largely concavely 

 arcuated in front, causing the auricles to be pointed, and gra- 

 dually tapers to a subtriangular termination. The usual oper- 

 culum of the tribe is carried on a simple lobe in an advanced 

 position neai'ly at the junction of the foot with the body. The 

 animal is vivacious, displays the eyes on the march, and makes 

 rapid progression ; it is only obtained at Exmouth in the coral- 

 line zone, and is rare. 



Chemnitzia diaphana. 



Rissoa ? diaphana, R. glabra. Alder. 

 Jeffrey sia diaphana, nonnull. 



Animal inhabiting a spiral shell of four and a half tumid vo- 

 lutions. Mantle pale yellow, even with the shell. The head is 

 short and flat, and so deeply cloven as to form two distinct flake- 

 white divergent spatulate lobes with the mouth at the angle of 

 the fissure ; these processes have the appearance of a pair of ten- 

 tacula, but the true ones are external to them, of hyaline flake- 

 white, not very slender nor pointed, and are rather longer than 

 the pseudo-tentacula. The eyes are large, black, placed very 

 far back on small, very little raised eminences, surrounded by a 

 lucid spot or circle issuing from the skin a little within the in- 

 ternal portion of the bases of the tentacula ; they are never ex- 

 posed, but always carried on the march within the shell, where, 

 from its hyaline nature, they can easily be seen. Foot rather 

 long, but not slender, auricled in front, gradually tapering to a 

 rounded point without any sort of caudal appendage, but has a 

 slight longitudinal medial line on the under surface : the usual 

 corneous operculum is placed at a little distance from the poste- 

 rior upper termination of a simple operculigerous lobe ; it is of 

 suboval form, pointed at one end and rounded at the other ; it 

 has marked strise of increment proceeding from a minute apo- 

 physis which is the nucleus j it is of very pale colour. We have 

 omitted to mention that the operculigerous lobe extends laterally 

 a trifle beyond the pedal disk, forming very narrow arcuated seg- 

 ments. The whole of the foot beneath, as well as at the poste- 

 rior end above, is pale yellow, but the upper anterior portion 

 with the neck and head, from the mouth posteally, is marked 

 with excessively minute close-set red-brown points. The three 

 posterior volutions are occupied by the viscera, comprising an in- 

 tensely dark red-brown liver, which, with the ovarium between 

 the lobes, are very conspicuous through the tenuity of the shell. 



The animal is not shy; it shows the organs freely and marches 

 with vivacity; it also swims and floats with perfect ease, as is 



