262 BULLETIN: 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 1887, 
had reached a similar conclusion in regard to Chimaera. The following is a 
repetition of his statement. 
“The development of the prehensile organ on the upper part of the snout, which 
is peculiar to the male sex in Chimaera, keeps pace with that of the claspers. This 
organ is visible in our youngest specimen, which 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 1s an accessory sexual organ, in its inception in 
all probability merely a transverse fold of the skin of the forehead. If 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 exhibit 
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 sufliciently 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 the 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. IT., 
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 in 
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. Not 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 
