JURASSIC CHIM.i;ROIDS. 



141 



and extended in 

 their lines of attach- 

 ment forward as far 



as the antero-lateral clasping organ.* 

 This is of particular interest, since it in- 

 dicates, as we have alread}' noted, that 

 the antero-lateral clasping organ was 

 probably, as Gegenbaur, Garman, and 

 Agassiz suggested, a modified radial car- 

 tilage (possibly a number of radial car- 

 tilages), but up to the present time 

 there has been no evidence which has 

 bridged the wide gap between the antero- 

 ventral clasper and the true radial 

 cartilages. The condition of the mixip- 

 terygium is also significant, for it is here 

 short and wide, its base in one specimen 

 suggesting clearly its origin in a cluster 

 of radial cartilages. One observes, also, 

 that the shagreen which encases this 

 organ is not limited to its tip, but extends 

 proximally almost to its base, a condition 

 which has been retained so completely 

 in no living Chimairoid. It may be 

 noted, finally, that a mucous-canal sys- 

 tem is present whose supports are 

 arranged in rouleaux of minute rings, a 

 condition which exists in a somewhat 

 rudimentary form in recent genera. 



Summarizing, then, our knowledge 

 of Squaloraja, we find that this early 

 Chimseroid was shark-like in the follow- 

 ing regards: (i) In dermal defenses, 

 exhibiting as it does an investiture of 

 shagreen. (2) In the width of the mouth, 

 which shows definitely that it had not 

 yet attained the beak-like character of 

 the mouth of recent forms. (3) In the 

 undifferentiated condition of the clasp- 



133 



m 



'S^S&^^S^ 



135 



ing organs. 



The frontal clasper is still a 



Figs. 132-137. — Evolution of frontal clasping spine ot Chim- 



aeroids, 



132. Fir-spine o( Myriacanlhus. 133. Frontal clasping spine o( Squalo- 

 raja. !34. Frontal clasping spine of Myriacanthus. 134 A. Base 

 of clasping spine of Myriacanthus, ventral aspect, to show areas of 

 attachment of muscles. 135. Frontal clasping spine of Ischyodus. 

 after specimen in Munich Museum. 136, Frontal clasping spine 

 of Chimtra. after section given by O. M. Reis. I 37. Frontal 

 clasping spine of Squaloraja. dorsal aspect. I37A. Ventral view 

 of base, showing areas of attachment of muscles. 



*This was observed by the writer in a specimen (P 2276) in the British Museum earlier described by Smith Wood- 

 ward. Dr. Woodward did not, however, note that these clasping organs were present, although figuring them as 

 "remarkably strong prepubic processes." Each clasper has appended denticles, of which as many as eleven were prob- 

 ably present. The same specimen has preserved in outline visceral structures, apparently testes and vasa deferentia. 



