246 BULLETIN : MUSEUM OF COMPARATIVE Z05lOGY. 



A new geuus, Ehiiiochimaera, is established, also a new family, Rhino- 

 chimaeridae, to contain Riiiuochimaera and Harriotta, and still another 

 new family, Callorhyuchidae, 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 in 

 Callorhynclius 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 wliich tlie 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 rpceut 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- 

 dout 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 oric- 

 inated from the indurated membranes of the jaws, or their hardened 

 papillae. 



To judge from the dentition alone, the extinct Myriacanths were 

 Yiearer the ancestral stem on which farther back tlie 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 Callorhynchus, 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 cliaracters as they become mature; 

 a frontal tenaculum and two ventral tenacula are developed as the 

 claspers approach functional maturity. 



A more primitive form of tlie frontal tenaculum is that of the extinct 

 form Sqnaloraia; in its inception the organ was merely a transverse fold 

 of the skin on the forehead. 



The frontal tenaculum, being a sexual character, is not to be homolo- 



