46 systematic arrangement 



3. Marsenina. 

 Body convex ; mantle edge swollen, covering the edge of the shell. 

 Shell spiral, ear-shaped, the external part covered. Teeth 3* 1*3; 

 central rather elongate, broad, with a reflexed denticulated tip ; inner 

 lateral broad, with a triangular curved toothed tip, or outer lateral 

 linear— Berg, t. 4. f. 14, 15. 



1. M. micromphala, Berg, Marsen, t. 4. Fis * 26# 



2. M. prodita. Lamellaria prodita, Loven. Marsenina prodita. 



3. ? M. plicatilis, Forbes ty Hanley, B. M. 



t. O.O. f. 8, foot produced in front. 



"The edge of the mantle of M. plicatilis 

 is produced beyond and partly covering the 

 shell."— Miiller. ( = Velutella, Gray.) 



Central tooth of Marsenina prodita elevated, upper part rounded, 

 wider ; cutting edge transverse, with one sharp point, minutely 

 toothed on each side ; lateral teeth suberect, somewhat similar, claw- 

 like; inner side of the first and second furnished with a minute 

 tooth before the bend (fig. 26). 



** Shell internally convex, not spiral. 



4. Onchidiopsis. 



Body spherical, inflated. Shell internal, horny, not spiral. Teeth 

 3 • 1 * 3 ; central broad ; apex reflexed, dentated ; inner lateral broad, 

 with an elongated reflexed toothed tip ; two outer linear hooked. — 

 Berg, t. 2. f. 15, 16. 



1. O. Groenlandica, Berg, Marsen, t. 2. 



2. O. carnea, Berg, Mai°sen, t. 3. 



D. Mantle not siphoned, enclosed. Mouth of shell entire in front. 

 Shell sunk into the large foot of the animal (p. 37, 44). 



Fam. XVIII. NATICIDJE. 



Foot very large, much produced in front, as if formed of four 

 lobes, partly covering the shell, which is sunk into its substance. 

 Mantle enclosed. Operculum spiral, horny, sometimes covered with 

 a shelly external coat. 



Foot folded, so as to form a round canal to admit the water to the 

 gill-cavity on the left side of the shell. — See Foy. Bonite, t. 35. 



Eyes, when present, immersed in the skin at the centre of the an- 

 terior base of the tentacles. 



The ^ills consist of two plumes and some mucous fillets. Muzzle 

 elongated, entirely retractile. Opercular mantle very large. 



The trunk of Naticidce is elongate, quite retractile. Tentacles 

 united by a transverse membrane ; eye-peduncles immersed at the 

 outer base of the tentacles; chin very large; opercular lobe very 



