262 BULLETIX: MUSEUM OF COMPARATIVE ZOOLOGY. 



its period of utility in the congress of the sexes. This was in relation to all 

 the genera of the group. It was overlooked at the time that Giinther, in 188 7, 

 had reached a similar conclusion in regard to Chimaera. The following is a 

 repetition of his statement. 



" The development of ttie prehensile organ on tlie upper part of the snout, which 

 is peculiar to tlie male sex in Chimaera, keeps pace with tliat of the claspers. This 

 organ is visible in our youngest specimen, wliich evidently was hatched only a few 

 days, as a narrow cartilage of whitish colour entirely covered by the skin, but 

 visible through it. It has not made as great progress in the largest of the young 

 specimens, and therefore does not seem to become detached from the head before 

 the individual attains to sexual maturity." 



" Detached from the head " in this may mean either detached from the skull, 

 or attains to partial freedom above the skin, probably the latter. 



The frontal tenaculum of the Chimaeroid male is not a modification of a fin 

 ray, as in the Pediculati, but is an accessory sexual organ, in its inception in 

 all probalulity merely a transverse fold of the skin of the forehead. ]f it were 

 a modification of a fin spine or radial, it would at the first appear as such, 

 without waiting for sexual maturity, and the embryo would be likely to exldbit 

 traces of its evolution. The frontal tenaculum of Squaloraia, a fossil from the 

 Lower Lias, is to be regarded as an intermediate form between the primary 

 transverse fold and the much-differentiated frontal tenacula of the living 

 Chimaeroids. In the fossil the base of the organ is transverse, and without 

 the simple elongate slender distal portion would sufficiently resemble a trans- 

 verse fold. 



Naturally the higher groups are less clearly outlined in the fossil forms than 

 in the recent, and the farther back attempts are made to distinguish them, 

 along the converging lines to a common ancestry, the less definite the dis- 

 tinctions, until among tlie earlier they may not be recognized, and the more 

 prominent and numerous the intergradations. The modern tendency of empha- 

 sizing divergent features leads to multiplication in the number of families. 

 "Woodward, 1891, in the Catalogue of Fossils in the British Museum, Vol. II., 

 distributes the Chimaeroids in four families, Ptyctodontidae, Squaloraiidae, 

 Myriacanthidae, and Chimaeridae. Only the last of these contained species 

 that are now living. If the recent forms are arranged in three families, as ia 

 the present writing and in the preliminary, Rhinochimaeridae, Callorhynchi- 

 dae, and Chimaeridae, the known fossil species will be distributed in five fami- 

 lies, by leaving Chimaera pliocenica and C. javana in the Chimaeridae, and 

 placing Callorhynchus hectori in the Callorhynchidae. Undoubtedly future 

 studies will increase the number of families to which even the known fossils 

 are credited. Kot much can be done in comparing the recent with the extinct 

 forms, since so little is known of the latter. In most cases the fact of existence 

 has been established only through remnants of the dental apparatus. Of the 

 characterized families the Ptyctodontidae are distinguished by two pairs of 

 teeth, one above and one below, and no spines are known ; the Squaloraiidae 



