200 



CARNEGIE INSTITUTION OF WASHINGTON. 



At the Tortugas, the colonies on Loggerhead Key were in better condition 

 than I have seen them on any previous visit. In fact, I beheve more of 

 Cerion viaregis and Cerion casahlancce exist on Loggerhead Key to-day than 

 in their native habitat. The only effect that the hurricane has apparently 

 had upon our colonies at the Tortugas is that the water carried some of the 

 specimens a considerable distance from the place where they were planted, 

 so that it is quite possible that in the future there may be considerable inter- 

 minghng of the animals in various parts of the islands. 



The colony of Cerion iwa is just beginning to show adult specimens. This 

 shows a much longer developmental period than is the case in the Bahaman 

 species. Of the latter, as stated before, we were able to obtain mature genera- 

 tions in three years, while the Cerion uva colony was planted in May 1916, 

 which indicates five years as a developmental period. 



In the report "Experiments in the breeding of cerions," Department of 

 Marine Biology, Carnegie Institution, vol. xiv, 1920, we gave on page 46 

 detailed measurements of 100 specimens representing the check series of 

 Cerion crassilabris from Balena Point, near Guanica Bay, Porto Rico, which 

 were planted on Loggerhead Key in 1915. These were figured on plates 

 48 to 50. On page 47 we gave measurements, and on plate 51 figures of 36 

 adult shells of the first Florida-grown generation gathered in January 1919. 

 This year we found a much larger series of first-generation material, and the 

 following table gives a summary of measurements of 200 of such specimens: 



Comparison of measurements of Florida-grown Cerion crassilabris with the check series. 



It is interesting, therefore, to note that the first generation of this Porto 

 Rican cerion is in complete agreement with the facts adduced from the two 

 Bahaman species. 



The hurricane of 1919 destroyed the cages in which we had placed a speci- 

 men 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 we 

 placed a HymenocalUs plant, some grass and dead-wood rubbish, in other 

 words, habitat conditions which we found favored by cerions at the Tortugas. 

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

 incanum from Key West, were placed in each of the 44 compartments. These 

 cages are securely anchored, and every precaution has been taken to make 

 sure that the mollusks will be confined within them, and that no extraneous 

 individuals can find entrance. 



