CHAP. IV. 



SCAPHELLA 



TYPES OF FORM. 



123 



V. rarispina we can only form our conclusions from 

 the figure in Ency. Mtth. 384. fig. 2. It would seem 

 from this, that there is a very distinct sinus at the base 

 of the outer lip, while the wide-spread deposition of 

 enamel on the inner lip reminds us both of the genus 

 Marginella and of Voluta Scapha : it is, in short_, the 

 strombiform type. 



(111.) We now come to the last genus, Scaphella. 

 Although these shells are readily distinguished by the 

 experienced malacologist at the first glance, it is not so 

 easy to define them by words. Their true characters, 

 we apprehend, will be found in the animal. They 

 differ from all other known volutes, by being always 

 without sculpture, and generally polished like the Mar- 

 ginellce. The apex of the spire varies precisely in the 

 same way as in the genus Harpula : in the chief type, 

 represented by S. undulata, it is small, and obtusely 

 pointed. In fusiformis, it is decidedly thick ; and 

 in papulosa, it becomes exceedingly large and round. 

 A shelly deposition is often formed in mature age, at 

 that part of the outer lip which joins the spire, and 

 also on the pillar side of the aperture : there is a con- 

 stant propensity, in short, to this thickening of the 

 pillar, even in shells which usually have their plaits 

 distinct. The first advance to this structure, after 

 leaving the last genus, is by a very singular fossil shell, 

 described by Lamarck as the Buccinum strombio'ides. 



11 



( fig. 12. a, b.) Mr. G. B. Sowerby, in adopting this name, 

 justly observes, that, but for the absence of folds on the 



