84 . PTERONOTl S. 



Sub-genus Pteronotus, Swainson. 



This group may be advantageously restricted to those species 

 possessing a muricoid operculum and three varices. Its position 

 is somewhat difficult to define, inasmuch as its relationships are 

 varied with Cliicoreus rather than with Phyllonotus perhaps, and 

 on the other hand with Gerostoma : which latter may include 

 the forms, likewise with three varices, with or without the lip- 

 spine w r hich Conrad makes the t} T pical character of his group, 

 but with purpuroid operculum, and in general aspect forcibly 

 suggesting a connecting link with Pttr/ira. Kobelt has indeed, 

 included such species as Purpura plicata and lactuca in his group 

 of Cerostoma,, but I think the line between the Purpuroid Muri- 

 ces and Purpura proper may be drawn just here, if anywhere 

 that Gerostoma is a normal Murex in its three continuous varices; 

 whilst the numerous varices of P. plicata and its allies insensibly 

 degenerate into shells without varices = typical Purpurse. 



It may be remarked that Pteronotus, as thus restricted, consists 

 of East Indian and African species, whilst the distribution of 

 Cerontoma is North Pacific, extending from the west coast of 

 North America to Japan. 



a. With two or three ribs or tubercles between the varices. 



M. TRIGONULUS, Lam. PI. 11, fig. 120. 



Owing to the insufficiency of the original description and the 

 want of reference to a published figure this species has been 

 variously identified with several others since described. I prefer 

 the decision of Reeve, because it relieves these other species 

 from doubt. Kobelt gives "Antilles " as locality, which shows 

 that he has supposed it related to the motacilla or recur cirostris 

 group- which it certainly does somewhat resemble. Tapparone 

 in quoting it from the Red Sea, confounds it withtriqueter, Born, 

 and Sowerby figures for it (Conch. 111.) an example of M. pel- 

 lucidus, Reeve. It will be seen that the form selected by Reeve 

 to represent the species stands intermediate between M. recurci- 

 rostria and M. triqueter. I have before me a specimen said to 

 come from Gambia. The shell is rosy-white, with two darker 

 bands. 



Length, 1-5 inches. 



