NO. 15 SMITHSONIAN EXPLORATIONS, I92I 49 



Bay, Porto Rico, which were planted on Loggerhead Key in 1915. 

 These were figured on plates 48 to 50. On page 47 measurements 

 were given and on plate 51 figures of 36 adult shells of the first Florida 

 grown generation which were gathered in January, 1919. This year a 

 much larger series of first generation material was found, and 200 of 

 such specimens were measured. 



The summaries of these measurements show that no appreciable 

 changes in measurements have taken place in the first generation of 

 Florida grown Ccrion crassilabris. The measurements in size all fall 

 within the limits of variation, as denoted in the check series, excepting 

 one, 7'. e., sl single specimen which was found among the 200 of the first 

 Florida grown generation that had a diameter 0.2 mm. less than any 

 in the check series. There is no doubt that one could find an indi- 

 vidual giving such a measurement among the specimens on the native 

 heath of this species, for the check series was not a selected one, but a 

 hundred specimens taken at random. 



COMPARISON OF MEASUREMENTS OF FIRST FLORIDA GROWN CERION 

 CRASSILAP.RIS WITH THE CHECK SERIES 



No. whorls 



Average &^''}' s^"^^. 9-55 



[birst generation 9.13 



Greatest diameter i gieck series _ 10.5 



L^irst generation 10.4 



Least diameter /Check series 8.5 



l^rirst generation 8.0 



It is interesting, therefore, to note that so far as the first genera- 

 tion of this Porto Rican Cerion is concerned, it is in complete agree- 

 ment with the facts adduced from the two Bahaman species. 



The hurricane of 1919 destroyed the cages in which had been placed 

 a specimen of each of two species, in order to determine their ability 

 to hybridize, and to note the results of such crosses as might be 

 observed from such selected individuals. 



A new set of cages was therefore prepared. Eleven groups of 

 these cages consist of four compartments, each a cubic yard in size. 

 The septa between compartments are double wire walls to prevent 

 possible mating through the meshes of the fine Monel metal wire 

 screen. In each of these cages there were placed a Hymenocallis 

 plant, some grass and dead wood rubbish, in other words, habitat 

 conditions which were found to be favored by Cerions at the Tortugas. 

 Then two half-grown specimens, one of Cerion znarcgis and one of 

 Cerion incanum from Key West, were placed in each of the forty-four 



