in our form the female is orange color while the male is Naples yellow. 

 In the male the lateral tentacles are shorter than those of the female. 

 At Ironbound Island I collected all the specimens in a restricted 

 locality and found 220 females and 164 males. Jeffreys, in his 

 "British Conchology," describes the creature as having six tentacles 

 on a side. Despite these slight differences they may be regarded as 

 geographical variations. The early stages of the shell resemble so 

 strongly Vitrinella that some of the species described as Vitrinella 

 from the West Coast and other regions may turn out to be the young 

 of some species of Margarita (P. VIII. Fig. 10 B.) 



TROCHUS OCCIDENTALIS Migh-Adams 

 PL II. Fig. 11. Diameter 12 mni. 



This beautiful species is a rare form on our coast, it is also very 

 rare in England, according to Forbes and Hanley, through Jeffreys 

 says it is not uncommon in some places. Forbes and Hanley identify 

 this shell as the T. alabastrum, and places occidentalis among the 

 synonyms, adding, however, that "should it prove the Trochus occi- 

 dentalis of North America, as judging from the description, we think 

 likely enough, that name must be substituted for Beck's." Jeffreys 

 (1865) recognizes T. alabastrum as T. occidentalis, and Dr. G. O. 

 Sars, in his fine work entitled "Mollusca Regionis Arcticse Norvegiae," 

 published in 1878, recognizes T. alabastrum, of Beck, as T. occidentalis, 

 of MiGHELS. The English form as described by Forbes and Hanley 

 differs somewhat from our form. The animal is described as "entirely 

 pure white," while our species is yellowish white, mottled with brown- 

 ish granules, the creeping disk orange. T. alabastrum, according to 

 Forbes and Hanley, has three lateral tentacles on a side. Jeffreys 

 says, "appendages three (sometimes four) on each side, resembling the 

 tentacles in every respect except in being smaller." The few speci- 

 mens of T. occidentalis that I was able to observe had four tentacles 

 on a side. 



The shell of T. alabastrum of England and Norway very closely 

 resembles the T. occidentalis of our coast. The revolving ribs are 



8 



