Miscellaneous. 147 
Triassic period ; and that the rareness of Triassic fossils was due not 
so much to the paucity of animal life during that period as to the 
fact that Triassic strata afforded no suitable conditions for the pre- 
servation of organic remains. 
MISCELLANEOUS. 
On the so-called Dimorphism in the Genus Cambarus. 
By Watrter Faxon. 
Tue existence of two forms of the adult male in all the species 
of the genus Cumbarus was discovered by Louis Agassiz and Henry 
James Clark. The differences between the two forms affect more 
especially the first pair of abdominal appendages, organs concerned 
in the act of coition, but also extend to the general form and sculp- 
ture of the body. In one form (unhappily called by Dr. Hagen the 
“second form’’), the first pair of abdominal appendages have a 
structure nearly like that seen in all young males. The hooks on 
the third joint of the third (in some species of the third and fourth) 
pair of legs are small, and in the sculpture of the shell and shape of 
the claws this form approaches the female. In the other form 
(Hagen’s “ first form”), the articulation near the base of the first 
pair of abdominal appendages is gone, and the whole member is 
much more highly specialized, the terminal hooks being horny, more 
widely separated, and in every way more highly developed; in 
those species with bifid tips to these appendages the branches are 
longer, slenderer, more widely separated, and stiffer; the hooks on 
the thoracic legs are longer and more perfectly finished ; the sculp- 
ture of the whole body is more pronounced, and the claws are larger 
and more powerful. No intermediate conditions are found, and 
there is no relation between these forms and the size of the indivi- 
dual, the ‘‘ second form ” being large and the “first form” small, 
or vice versd. Hence we are forbidden to interpret the two forms 
as stages in ordinary development. Dr. Hagen has shown that in 
individuals of the “second form” the internal generative organs are 
smaller than in the “first form,” but having only alcoholic material 
he was unable to determine any thing concerning the presence or 
absence of spermatozoa. He interprets the facts asa case of dimor- 
phism, and surmises that the “second form” males are sterile 
individuals. 
In the autumn of 1875 I received a lot of living Cambarus rusti- 
eus, Girard, from Kentucky, males of the “ first form” and females, 
which bred freely in confinement. After pairing, three of the males 
moulted, and were thrown, while in the soft-shelled state, into 
alcohol, together with their exuvie. An examination of these 
Specimens now reveals the fact that the soft-shelled specimens are 
