184 Miscellaneous. 
from this he argues that they died in their natural position, and 
that when living they probably swam on their backs. He men- 
tions, in support of his view, the well-known fact that very young 
Limuli and other Crustacea frequently swim in that position. I 
have for several summers kept young horseshoe crabs in my jars, 
and have noticed that, besides thus often swimming on their backs, 
they will remain in a similar position for hours, perfectly quiet, on 
the bottom of the jars where they are kept. When they cast their 
skin it invariably keeps the same attitude on the bottom of the jar. 
It is not an uncommon thing to find on beaches, where Limulus is 
common, hundreds of skins thrown up and left dry by the tide, the 
greater part of which are turned on their backs. An additional 
point to be brought forward to show that the Trilobites probably 
pass the greater part of their life on their back and die in that 
attitude, is that the young Zimuli generally feed while turned on 
their back; moving at an angle with the bottom, the hind extre- 
mity raised, they throw out their feet beyond the anterior edge of 
the carapace, browsing, as it were, upon what they find in their 
road, and washing away what they do not need by means of a 
powerful current produced by their abdominal appendages.—Szll- 
man’s Amer. Journ., Jan. 1878. 
New Species of Ceratodus from the Jurassic. By O. C. Manrsu. 
Among the interesting vertebrate remains recently found in the 
Jurassic of Colorado is a tooth of a Ceratodus in good preservation. 
The specimen is a left lower dental plate, having the inner side 
convex, and the outer divided into five prominent projections, which 
are separated by four notches. The front projection is longest and 
most pointed. The plate is attached fo a portion of the dentary 
bone. 
The length of this dental plate is 20 millims., and the transverse 
diameter 11 millims. The species is the first Mesozoic Ceratodus 
found in this country, and hence of much interest. It may be 
named Ceratodus Giinthert, in honour of Dr. A. Gunther of the 
British Museum. The geological horizon of this species is in the 
Atlantosaurus beds of the Upper Jurassic.—Silliman’s Amer. Jeurn., 
Jan. 1878. 
Sexual Dimorphism in Butterflies. 
Mr. S. H. Scudder, in an article on sexual dimorphism in butter- 
flies (to which special kind of dimorphism he applies the term anti- 
geny), states that it isnot the male but the female that departs from 
the normal type of colouring of the group to which the species 
belongs, while it is the male that shows divergences from the type 
in structural characters. These structural divergences in butterflies 
appear in the wings and the legs, and sometimes in the antenne. 
Mr. Scudder knows of no example in which the male alone diverges 
from the general plan of coloration belonging to the group.—Proc. 
Amer, Acad. 1877. 
