19 2 MESSRS. R. J. L. GUPPY AND J. HOGG ON THE 



We shall first premise that the teeth on the dental band of the Mollusca are mostly 

 disposed in longitudinal series. In the Pnlmonata there is usually a single median row, 

 the laterals on each side being broad and similar. But in most of the other groups 



arranged in three, five, or seven dissimilar series. Taking Nerita or 



teeth are 



llelieina as a type, we designate as laterals the broad teeth on each side of the median 

 row, the numerous small teeth on the outside of the band being known as pleural ; and 

 t he teeth on this are termed uncini. The latter are found only in certain groups. Most 

 of the Mollusca mentioned in this paper have been recently described or enumerated in the 

 4 Annals and Magazine of Natural History'*, where further particulars as to their habits 



and organization will be found. 



In the genus Bulimus we have a dentition resembling in general characters that of 

 Helix— that is to say, a broad dental band with numerous similar teeth. But the forms 

 of the teeth themselves are very varied ; and it is a subject for inquiry how far the divi- 

 sions proposed by zoologists are borne out by this part of the organization. In Bulimus 

 oblongus the teeth are subquadrate, with simple obtuse cusps, the laterals differing but 

 slightly in shape and size from the medians. This species is interesting on account of 

 the peculiar frontal appendages, first described by D'Orbigny, which recall to our minds 

 those of the Nautilus, though the resemblance is not perhaps great ; still it is a morpho- 

 logical resemblance. We find, too, that this mollusk has mandibles somewhat resembling 



those of a Cephalopod. 



The teeth of Bulimus zebra have considerable resemblance to the preceding. The 

 animal has no peculiar frontal appendages, like those of B. oblongus; and its mandible is 

 not different from those of other members of the group. 



Bulimus virgulatus, a mollusk of the Antilles, presents a different type. The teetl 



are in divergent rows, the medians small, with a round reflexed tricuspid point, the 



laterals, on subquadrate bases, with denticulate reflexed edges, the cusp on the inner 

 side being rather long. The denticles appear to be 3-4 in number, of which two only 

 are usually seen at one view with the microscope. 



The teeth of Bulimus multifasciatus (Plate XI. fig. 1), B. immaculatns, and B. aureolas 

 are so nearly alike, that one description will serve for them all. In general arrange- 

 ment they are like the preceding species' ; but the medians are minute, and the laterals 

 are armed with three long acute cusps, which frequently escape observation, being as 

 pellucid as glass. We have ourselves overlooked them; and owing to this the teeth of 

 this species have on former occasions been wrongly described. 



In Bulimus caracasensis the medians, so extremely difficult to make out from their 

 minuteness, are simple, the laterals symmetrical ; that is, they are equal-sided, differing in 

 this respect from those of most other mollusks. We have observed that several of the spe- 

 cies classed under Bulimus present this form of teeth, which is also found in Stenogyra 



octona (fig. 2). In Tornatellina lamellata (fig. 5) the dentition somewhat resemble 



that of Bulimus multifasciatus, the laterals having long acute pellucid cusps. 

 In Plecocheilus auris-sciuri (fig. 4), a species very near P. glaber, the median 



* Ser. 3, vol. xiv. p. 243, and vol. xvii. p, 42. 



