PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 47 



sculpture is that of II. rv/cscens ; the radiating sculpture, except that it 

 is not sharp or imbricated, recalls IL corrugatus, and the nacre is similar 

 but less bright. These characters suggest the possibility of its being 

 a hybrid between II. corriigatus and riifescens; but if this be the case, 

 why should it not have a similar habitat? Those two species are litto- 

 ral, but this is exclusively deep-water. I have received it from Dr. 

 Oanfield, Mrs. Capt. Lambert, and others, in past years, and have exam- 

 ined some twenty specimens of all ages. 



Acmasa (scabra var. ?) Morchii, n. s. 



Shell conical, much elevated, with a sub-central recurved apex resem- 

 bling that of Helcion pectinatus covered with close-set, rough, imbricated 

 ribs and riblets, the coarse, imbricated, sharp lines of growth forming 

 with the other sculpture a close reticulation in some specimens. Interior 

 with a brown-mottled spectrum and margin, otherwise white; exterior 

 dull grayish or greenish speckled. The imbrications on the principal 

 ribs very strong, in some specimens forming small spines concave 

 beneath. Lat. IG""". Lou. 20""". Alt. 10™'". 



Tomales Bay, California, Ilemphill, 16 specimens. Mus. Cat. 31268. 



This very peculiar form has the sculpture of A. scabra., but much 

 exaggerated, and very nearly the profile of Helcion pectbiatus. The 

 recurved apex recalls that of A. persona. It would not be referred to 

 any described Californian species if its characters, as they appear, were 

 the only test. But it is almost certain that all the species of Limpets 

 and Siphonaria', which have this peculiar elevated shape, acquire it 

 from a particular habitat which they seem to prefer. This may be the 

 stem of a large Fucus, a shell, round pebble, or what not, as in the case 

 of those species of Acmaa usually (but wrongly) termed Nacella by 

 Californian conchologists: Acnucaosmi ; Liriola sithspiralis ; etc. They 

 all have a flattened or normal variety, though this is often very rare. 



Hence I consider the elevated form and pointed apex as probably 

 due to a peculiar habitat, as in the other cases ; a view which is borne 

 out by a peculiar arcuation of the margin in most of the specimens, as 

 if the creature had lived on a round shell or pebble. 



Eliminating the elevation as a permanent character, the shell, appa- 

 rently very limited in its distribution, might well be a hybrid between 

 .1. scabra and A. persona. Whether this be the case or not, it is a very 

 remarkable form, and well deserves a name, even if only of varietal 

 value. We owe its discovery to Mr. Hemphill's industry and eminent 

 abilities as a collector. 



Afril 30, 1878. 



