MUSEUM OF COMPARATIVE ZOOLOGY. 243 



not perfectly adult, that the proper section to which they are to be referred, 

 except in the case of Bpecies collected alive and in large quantities, will neces- 

 sarily often remain doubtful. 



The variety in the sculpturing ia very remarkable, and the range of varia- 

 tion in this direction is as yet but little understood. 



Section TRIFORIS s. s. 



The only species definitely referable to this section within our limits is the 

 Triforis mirahilis C. B. Adams, which extends southward from the Carolina 

 coast to the Antilles, apparently not abundant anywhere. It has been errone- 

 ously confounded with T. turris-thomce Orbigny. 



Triforis lilacina Dall. 



Shell corpulent, acutely pointed, characterized by two spiral rows of round, 

 pointed, large elevated tubercles, about twenty-five on the last whorl; there 

 they are separated by a fine undulated line, while on the earlier whorls this is 

 obsolete or absent; there is a very fine post-sutural thread; whorls about 18, 

 of a rich pink lilac color, the tubercles a little lighter; base protuberant, with 

 four or five regularly beaded spiral threads; canal closed, much recurved, short; 

 anal notch deep, probably eventually tubular; mouth contracted, anterior edge 

 produced, aperture sharp-edged, simple. Max. Ion. of shell, 9.0; max. lat. of 

 shell, 2.9 mm. (Nucleus lost, probably pointed.) 



Habitat. Turtle Harbor, Florida, in 6 fms., Dr. Rush. 



This beautiful shell is nearest to ruber Hinds, which has smaller tubercles 

 and proportionally larger aperture. This and violacea Quoy (with fi.ve rows 

 of tubercles) are Indo-Pacific species. 



Section MASTONIA Hinds. 



A. Apex acute, trochoid. 



Triforis perversa Linne, var. nigrocincta Adams. 



Trochus perversus Linne, S. N., ed. xii. p. 1281. 

 Cerithium perversum Jeffreys, Brit. Conch., IV. p. 261, 1867. 

 Cerithium adversuw Forbes & Hanley, Brit. Moll., p. 195, pi. xci. figs. 5, 6. 

 Triforis perversa Jeffreys, P. Z. S. 1885, p. 67. 



Cerithium nigrocinctum C. B. Adams, Boston Journ. Nat. Hist., H. p. 286, pi. iv. fig, 

 11, 1839. 



Habitat. Barbados, 100 fms. Northward to Massachusetts. British Isles 

 to the Mediterranean. California ? 



After a careful study of specimens from both sides of the Atlantic, I con- 

 clude that the diS'erences which exist are far less than those which separate 



