246 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 
A new genus, Rhinochimaera, is established, also a new family, Rhino- 
chimaeridae, to contain Rhinochimaera and Harriotta, and still another 
new family, Callorhynchidae, to include the genus Callorhynchus. 
The body of Rhinochimaera is typical of that of most Chimaeroids; 
the proboscis is an ancestral feature that has become much reduced iu 
Callorhynchus and is obsolescent in Chimaera. 
The rostral cartilages are articulated to the skull and are not prolon- 
gations of it, as in certain Platosomia, Raiae, or in Antacea, Sharks, on 
some of which the rostral cartilages resemble a tripod, but with two legs 
superior, unlike Chimaeroids. 
The nearest approach, so far as noted, of recent Chimaeroids to Pla- 
giostomes, as attested by brains, dorsal spines, etc., is made toward 
Squalus and Heterodontus of the Antacea. 
The teeth of Rhinochimaera resemble the embryonic and ancestral 
more than those of the other recent genera of Chimaeriforms ; they are 
cutters rather than grinders, and probably are most like those of the 
Myriacanths and Rhyncodonts among the fossils. 
In Harriotta the tritors are grouped like the grinders of certain Placo- 
dont fishes more than those of other Chimaeroids. 
The tritors originated on the horny dental plate through stress 
or impact, much as the molars of Placodonts and others were orig- 
inated from the indurated membranes of the jaws, or their hardened 
papillae. 
To judge from the dentition alone, the extinct Myriacanths were 
nearer the ancestral stem on which farther back the four-toothed forms 
Rhynchodus and Rhamphodus may likewise be found. 
The brain of Rhinochimaera, like its rostrum, is nearer that of Callo- 
rhynchus than to that of Chimaera, reduction in the head of the last 
having brought the hemispheres and the olfactory lobes in contact. 
The notochord of Rhinochimaera is provided with rings like that of 
Chimaera ; it is unlike that of Callorbynchus, which shows no rings and 
is probably the more primitive type. 
The males of living Chimaeroids are subject to a certain metamor- 
phosis in acquiring secondary sexual characters as they become mature ; 
a frontal tenaculum and two ventral tenacula are developed as the 
claspers approach functional maturity. 
A more primitive form of the frontal tenaculum is that of the extinct 
form Squaloraia ; in its inception the organ was merely a transverse fold 
of the skin ou the forehead. 
The frontal tenaculum, being a sexual character, is not to be homolo- 
