OF MOLLUSCA. 



165 



ff Shell more or less exposed. Anal slit simple within. 



8. RlMULA. 



Shell conical, cancellated and radiately ribbed; apex elevated, 

 recurved, entire, a linear perforation on the upper part of the front 

 side, half-way between the margin and vertex ; mouth crenulated on 

 the edge ; cavity simple, without any shelly plate ; muscular scar 

 crescentic, interrupted in front. Living in sandy mud. 



1. R. exquisita, A. Adams, P. Z. S. 1851, 226. 



2. R. conica, D'Orb. Amer. Merid. t. 78. f. 10, shell only. 



9. Macroschisma. 



Animal narrow, elongate, with the shell near the hinder end. 

 Shell oblong, elongate, radiately striated, elevated, and subtruncate 

 in front ; apex anterior ; anal aperture large, elongate, on the front 

 slope of the shell. 



1. M. maxima, A. Adams, t. 51. f. 5. 



" The shell is on the hinder end of a very elongated body, like 

 Testacellus, not wider than the shell." — Cuming. 



Fissuridea (pileus) has a subconic, cap- like shell, with the apex 

 near the hinder margin, and a narrow perforation. 



10. Fissurella. 



Shell conical, radiately ribbed ; apex subanterior or central ; anal 

 perforation oblong, subapical ; aperture wide, oblong ; cavity simple ; 

 mantle enclosed, bearded on the edge ; anal siphon short, projecting. 



1. F. costata, t. 43*. f. 1-4. 



2. F. radiosa, t. 43*. f. 5, t. 113. f. 1. 



3. F. grseca?, t. 112. f. 1, t. 113. f. 6, 7; young, t. 113. f. 4. F. 



reticulata, Forbes fy Hanley, B. M. t. B.B. f. 7. 



4. F. patagonica, t. 113. f. 2. 



5. F. maxima, t. 113. f. 3. 



The shell of the young animal is entire, subspiral, with a per- 

 foration in front of the subspiral apex, which is at length de- 

 stroyed by the extension backwards of the anal perforation. 



Fig. 89.— Teeth of Fissurella. 



Lingual membrane of Fissurella elongate, broad, linear. Teeth : 



