CHAP. V. PTEROCERA. STR03IBUS. 139 



atus, but which we now remove to the present genus. 

 This we also do with the Strombus latissimus of authors, 

 which constitutes our fourth type. This remarkable 

 shell immediately follows the Pterocera sinuata ; and 

 although the digitations no longer appear, they are 

 slightly indicated by little folds : the side of the outer 

 lip, as in all the other types, is broadly reflected inwards. 

 In the fifth and last form, as seen in P. chiragra, the 

 digitations are again developed ; but they are fewer in 

 number, and of nearly equal length. In this type, also, 

 the basal channel is recurved outward ; and the sinus 

 on the lip is so remote from the base, as to admit of an 

 intervening process. 



(128.) The restricted genus Strombus follows that 

 of Pterocera ; it is distinguished by the outer lip being 

 entire, much dilated, and always furnished with sinu- 

 osities, or lobes, both above and below : the base is 

 short, and slightly turned upwards. In this genus there 

 are five distinct modifications. The Pterocera sinuata 

 leads us immediately to the first type, which is com- 

 posed of S.melanostomus, pacificus, Auris-Dianw hinn., 

 and Lamarckii* In all these, we trace the last rem- 

 nant of the character oi Pterocera, — namely, the folding 

 back of the outer lip, which is particularly conspicuous 

 in our ^S". melanostomus and Pacificus : the upper part, 

 also, is prolonged into a lengthened process. As a group, 

 it is at once known by the basal canal being turned 

 back, as in the Cerithince, or rabbit-shells. From these, 

 by means of S. tricornis and Gallus, we are brought 

 to the beautiful pink-mouthed S. gigas, and the rare 

 iS". Goliathus, where the lip may be said to have attained 

 its majcimum. In Acclpiter and Canai'um, it assumes 

 the shorter and more wing-like form of the type which 

 succeeds this : all these, with Strombus granulatus, &c., 

 and, finally, Epidi'omus, seem, to us, to constitute a 

 second type of form, w^herein the outer lip is particularly 

 large and spreading, yet without that short sinus, or 



* I know not who has affixed this name to what was considered the 

 smooth variety of Auris-Diarue. 



