TRANSACTIONS OF WAGNER 

 I 164 



TERTIARY FAUNA OF FLORIDA 



The Bermudian form has recently received a specific name from Miss 

 Bush (L. bermudensis Bush, Science, Aug. 25, 1899, p. 251). After examina- 

 tion of some hundreds of specimens from some forty localities, and careful 

 study of quite a number under a compound microscope, I have so far failed 

 to find any constant differences between the Bermuda shell and the ordinary 

 L. rubra. In a general way the former is a little rounder in form on the 

 average than the average rubra, but no more so than many British specimens. 

 The largest specimen I have seen, from the Channel Islands, is considerably 

 larger than the largest L. bermudensis I have found. As in nearly all cases, 

 however, the average specimens from southern waters will exceed in size 

 specimens of the same species from the north unless the species is boreal. 

 When we remember that southern Florida, as late as Miocene times, was 

 an island, and that Lascea is a species which does not appear to live on 

 purely sandy shores like those of the Carolinas, we can understand why the 

 species may have reached and flourished on the coral rocks of Bermuda while 

 it failed to progress northward on the mainland. 



In the separation of " species" much must be allowed for personal equa- 

 tion. Yet I cannot refrain from expressing the opinion that many of the more 

 interesting and important interrelations of animals must be lost sight of if we 

 subdivide beyond a certain limit. Some allowance must be made in any rational 

 system for individual variation in any given habitat, and for the other set of 

 variations which seem to depend upon geographical distribution. 



Small shells Hke Lascea, which attach themselves by a byssus to algae, may 

 be widely distributed by ocean currents. Differences of temperature and food 

 cannot fail to make their mark upon the different .colonies. When, in addi- 

 tion, we have a normal crudity and want of definition in the hinge characters 

 throughout the genus, it would seem inadvisable to subdivide the type too 

 minutely. 



The species has not yet been recorded as fossil in America, though very 

 probably it may be found hereafter in the Florida Pleistocene, as it has been 

 already in that of Europe. The group has been included here in order that 

 the treatment of the family may be as /jomplete as practicable. 



Lassea rubra (Montagu) Brown. 



The following measurements show the proportions of specimens from 

 various localities ; in each case the largest available specimen was measured, 

 not an average one : 



