136 SHELLS AND SHELL-FISH. PART I. 



small shells resembling Volvaria in form, but destitute 

 of any plaits upon the inner lip. The Cyprceidce will 

 thus form a group far less perfect in its contents than 

 the Volutidce, yet sufficiently marked to constitute it 

 circular. 



CHAP. V. 



THE PREBACEOUS GASTROPODS CONTINUED. THE STROMBID^, 



OR WING-SHELLS. 



(124.) The Strombid^ is one of the most varied of 

 the predaceous families, not so much in the structure 

 of the animals, as in their shells. The typical group, 

 indeed, is very peculiar in both respects ; but the 

 animals of the rest, with which we are as yet acquainted, 

 have a much greater sam.eness than would have been 

 expected from the marked difference in tlieir habitations. 

 In regard to the first, the most prevalent character 

 appears to be the pedunculated nature of the eyes, 

 which are generally situated about midway upon the 

 tentacula — never at their base, or at their tips. In 

 the typical Strombi, these organs are so much de- 

 veloped, that the iris is richly coloured ; and the eyes 

 of some of the large species have been described to us 

 as particularly beautiful. The shells present every 

 variety of the spiral form, excepting that they are never 

 depressed ; yet, throughout the whole, one character 

 may be traced : the outer lip is either enlarged, thick- 

 ened, or expanded ; or, if not so, the upper part is 

 detached from the spiral whorl, so as to form a Aving- 

 like or angular projection; hence their common name of 

 w;in^-shells : all are furnished with a small operculum, 

 and are strictly external shells. In the Lamarckian 

 genera Strombus, Conus, Columbella, Pleiirotoma, and 

 Cerithiurn, the student will see the five principal types. 



