140 THE NAUTILUS. 



large somewhat overgrown specimens, towards the margin of the 

 shells, the epidermis was somewhat rough, corresponding to the lines 

 of growth ; ijut then, not in the least presenting any such appear- 

 ance as shown by U. radiatus. 



As showing how variable in form U. hydianus is, the foUowing 

 measurements from two female specimens may be of interest. 



First specimen, length 61'5 mm., heiglit 42 nnn., diameter 36 mm. 

 Second specimen, length 55 mm., height 33 mm., diameter 20 mm. 



The great amount of this variation may be made clear to the eye, 

 by laying off on a line the length of the first specimen, on a line per- 

 pendicular to the first, lay off the diameter of the first specimen ; on 

 the same lines as axes, lay off the corresponding dimensions of the 

 second specimen. 



In this day of scientific enlightenment, men have come to look 

 upon chance as having no [)lace in Nature — but all is the outcome 

 of certain definite causes, which may often act in a complex manner. 

 Accordingly our friends in the botanical world have tried to explain 

 to us the origin and use of the varied beautiful forms and colors 

 that we find among flowers ; the entomologists try to explain to us 

 the origin and use of various colors — some sombre, some gaudy — that 

 we find in the insect world. A certain amount of study has been 

 put upon the origin and use of colors among marine molluscs ; and 

 dynamical causes have been proposed for structures found among 

 marine molluscs. Has anyone ever tried to account for the radia- 

 tions in our Unionidoi f or for the magnificent purple nacre of the 

 Uniones/)y(?7Jwrrt<?/s, graniferus or verrucosus f What is the origin 

 and use of the pustules, found in the many groups of Uiiionidw f 

 What is the origin and use of the plications in our various plicate 

 Unionidce f Also, have the adult Unionidce been found to have any 

 natural enemies, that feed upon them ? Do turtles ever eat vmssels, 

 might be asked. 



These are questions that no one is paying any attention to, seem- 

 ingly, and surely offer room for much work among students of 

 Unionidce. 



AVi: HAVE LATELY RECEIVED Specimens ol Helix vendryesi u. sp. 

 from Mr. T. D. A. Gockerell, of Kingston, Jamaica. The new 

 form closely resembles H. sloaneana, but is more depressed than 

 usual in that species, is more carinated, and of a very handsome 

 dark purple-brown color. It is from Montego Bay, Jamaica. — H. 

 A. P. 



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