POLYTROPA, 175 



P. emarginata, Desh. PI. 53, fig. 155. 



When the revolving ribs of saxicola or ostrina become broken 

 up into nodules, the result is P. emarginata, Desh., which is typi- 

 cally a very distinct looking shell, but connected by minute 

 gradations with the smoothest ostrina. It is a southern form, 

 P. Conradi, Nuttall MSS., is referred to it by P. P. Carpenter. 



P. LIMA, Mart. PI. 53, figs. 159, 156-158, 161. 



This is another form in which the typical variation from 

 lapillus is very great ; its characteristic appearance is due to a 

 considerable number of narrow, elevated revolving ribs, which 

 are alternately larger. The shell is usually so thin that the 

 external ribs form corresponding sulcatioris within the aperture. 

 The suture is frequently channelled, color light brown, more or 

 less banded and clouded with a deeper tint. Extends from Cali- 

 fornia northward to Alaska, and merges into fuscata and Frey- 

 cinetti on the one hand, and into saxicola on the other. P. 

 canaliculata, Duclos (fig. 156), P. attenuata, Reeve (fig. 158), P. 

 analoga, Forbes (fig. 157) and P. decemcostata, Midd. (fig. 161) 

 are synonymous. 



P. omspATA, Chemn. PI. 53, fig. 160 ; PL 54, figs. 163-166, 168. 

 This variet}' is well known under this name, but the work con- 

 taining the description only contains binomial phrases, as in this 

 case, accidentally. Murex plical, Marty n (fig. 165), is the 

 earliest binomial designation, and Buwinnui latnellosum, 

 Umelin. refers to the same shell, as do also Murex lactuca (fig. 

 163), and M. ferruginea (fig. 164), of Esch. It is a very thick 

 shell with long spire, the whorls more or less angulated by the 

 usually obsolete revolving ribs. At its southern limit on both 

 the California!! and Asiatic coast, it is comparatively smooth (P. 

 rupeslritt, Val. (fig. 160), septentrional s^ Rve. (fig. 160), Frey- 

 ciiietti, Liseh. (fig. 168), whilst at its northern limit the growth- 

 lines are occasionally developed into the lamellae which charac- 

 terize its most luxurious state. Outer lip very much thickened 

 within and dentate. Yellowish to reddish brown, with frequently a 

 central white band. Loves oysters, and has accompanied these 

 bivalves transplanted from Puget's Sound to Oakland, Cal. The 

 smoother form much resembles the vur. major of the European 

 lapillus. 



