194 MESSRS. R. J. L. GUPPY AND J. HOGG ON THE 



f omnia (fig. 8) and Adamsiella aripensis (fig. 10) . It would seem from this that the Cyclo- 

 stomatidse are probably not very closely related to the Littorinidee. Their lingual teetli 

 seem rather to point out an alliance with the Trochida?, or one of the groups possessing 

 pleura. But without attempting at present to decide this question, which can only be 

 determined by the examination of several species, we may remark that the Cyclostoma- 

 tiche will probably be found a natural and defined group, perhaps entitled to the rank 

 of a suborder, and not very closely related to any existing marine forms. 



The relations of the freshwater Operculata are as varied as are those of the land. Am- 

 pullaria doubtless finds its nearest marine relative in Ntttica,—*n opinion which seems 

 confirmed by the form of the shell. The dentition of Ampullaria vrceus and that of 

 A. effusa (fig. 13) are very much alike, and Marisa cornu-arietis (fig. 14) docs not differ 

 very greatly; the mandible is also similar, showing that the claims of the latter to 

 generic rank must be sought rather in the shape of the shell and the differences of the 

 siphons than in the teeth. Eydrobia spiralis appears to be akin to the Melaniidae ; but 

 we should not be surprised if it were found to be as close to Skene a. 



The horny mandibles of the Mullusca maybe deserving of some attention, with a view 

 to the elucidation of their affinities. In Cgolotus (tronslucidns) the mandible (fig. 11a) is 

 divided into two portions by a median articulation, and it is covered with fine acute 

 denticulations in regular rows*. In most of the Inoperculata the mandible is horseshoe- 

 shaped, and striate or corrugate. In Ampullaria the same organ is beak-shaped, like the 

 upper mandible of Octopus or Loligo. 



EXPLANATION OP PLATE X i . 

 Lingual Dentition of some West- Indian Gasteropoda. 



1. Bulimus multifasciatus, magnified 250 diameters. A wide band, £ of an inch in length, Cona»ting 



of numerous rows of similar teeth; medians with a central toothlct, and a smaller point on each 

 side; laterals in divergent rows, each with three toothlct , and an oblique, broadly reflex ed 

 cutting-edge. Mandible semicircular and corrugated. 

 Fig. la. Side view of central cusps. 



Fig. 2. Stenogyra octona, magnified 300 diameters. A narrow band, & of an inch in length ; medians 



simple, minute, inconspicuous, central cusps longest; lateral* tricuspid, with Central ensp much 

 prolonged. The ova of this species are subspherical, with i white testaceous envelope, some- 

 times remaining in the shell, whose aperture is thereby nearly filled up ; they hatch aft r the death 

 of the parent. 



Fig. 3. Maryinella carulescens, magnified 300 diameters. A band | of an inch long, of very pellucid, acute • 



pyramidal teeth; medians shorter than laterals ; laterals alternat ly a long and a short, set on 



f llO C?OYY.r\ v\lr%^,rw -> 1% ~ ~ ~ ~— X - 1_ 1 



membrane 



v 



ery pellucid. 



* Like Aptychus, but more horseshoe-shaped ; it is more probable that these problematical fossil* are the mandibles 



o Cephalopoda than the plates of their gizzards. They bear no resemblance in shape to the homy plates of the gizzard 

 of a mollusk. f ' r 



