548 H. B. POLLARD, 



5 ill Chac/ ostomus, which ])ractically runs ou to the shoulder- 

 girdle may represent its proximal portion. 



Comparison with the S e 1 a c h i i. If the foregoing comparison 

 of the Siluroids with Coccosteus is correct the latter is in certain re- 

 spects a link between the former and the Selachii. The following ac- 

 count of the resemblances is based upon Carman's description of the 

 distribution of the mucous canals in Selachii and llolocephala. The 

 interest lies chiefly in the infraorbital and opercular lines. It can 

 hardly be doubted that Heptanchus and Chlamydoselachus in which 

 the orbital (infraorbital) canal bends backward are the most primitive 

 forms. Chlamydoselachus is from Garman's description the best for 

 comparison. From the "orbital" at the back of the eye a line passes 

 horizontally backwards on to the mantle. This line is termed by 

 GAR^L\N the "angular". Some distance along its course it gives oö 

 a branch to the mandible the "oral". Continuing further it is termed 

 "jugular". After a short space it turns upwards and forwards as the 

 "spiracular" a branch turning down and then forward as the "gular", 

 this joining the oral. The space between orbital and oral is according 

 to Garman longer than is normal; he terms it "the long jugular". 

 Bearing this fact in mind it is surely not stretching the homologies 

 too far to recognize in the "oral" the groove in the suborbital of 

 Coccosteus marked 5, the homologue of branch 5 in Clarias. Further 

 the angular plus jugular represents the line in Coccosteus, numbered 



6 which passes from the infraorbital to the opercular, from the post- 

 orbital bone into the preopercular, and which corresponds to branch 6 

 in Clarias. Then the "spiracular" of Chlamydoselachus is the oper- 

 cular canal of Teleostei, and the "gular" corresponds possibly to the 

 downward branch in Coccosteus, the interopercular canal of Chaeto- 

 stomus, branch 8 of Auchenaspis and probably the terminal gular pit 

 line of Amia. In putting forward these homologies I do not mean to 

 assert that there is any close genetic relationship between Chlamydo- 

 selachus and Coccosteus. That I do not believe. 



An interesting parallel is offered in the transition from Polypterus 

 through fossil Crossopterygidae to Chlamydoselachus, which it may 

 be permissible here to recapitulate. In Polypterus the opercular canal 

 does not join the main canal. From the opercular canal in the middle 

 of the preoperculum a rudimentary branch extends forwards in a groove 

 in that bone. Anteriorly there are indications that it joined the infra- 

 orbital canal. In Osteolepis one of the fossil forms described by Pander, 

 the canal indicated by these rudiments is fully developed thus showing 



