LINKEAN SOCIETY OF LONDOX. 31 



Simplicity. The membrane of the dorsal fin, though subdivided 

 into two small remnants, is strengthened by simple parallel rods 

 of cartilage, which were doubtless supported by similar rods 

 between the muscles. The membranes of the paired fins are 

 similarly strengthened by parallel rods, each with a corresponding 

 support within the body-wall ; but instead of being notched at 

 the axil behind, they extend along the body and gradually taper 

 backwards beyond the strengthened part. The paired fins are, in 

 fact, obviously mere remnants of a once-continuous pair of folds.' 

 There is uo ordinary anal fin, but Dr. Bashford Dean * has 

 suggested that it may be represented by the pair of horizontal 

 lin-folds, supported within the body-wall by rods of cartilage, 

 occurring close to the base of the caudal fin, which is highly 

 specialised and heterocercal. The slime-canal of the lateral line, 

 as shown by the arrangement of the shagreen along its course, 

 must have been an open gi-oove. IStill more interesting, some of 

 the muscles and other soft parts are often preserved in the fossils, 

 and Dr. Dean f has identified the kidneys, showing their micro- 

 scopic structure, "extending remarkably far back beyond the pehic 

 fins. The body-cavity and the alimentary canal must therefore 

 have extended backwards as far as the end of the tail, thus 

 fulfilling Y. M. Balfour's prediction fi*om embryology that this 

 condition would eventually be found in primitive vertebrates. 



The identification of the kidneys is especially important, 

 because in one specimen of Cladoselache l<:ej)lcri in the British 

 Museum (no. P. 9269) they are displaced by crushing behind the 

 pelvic fins in such a manner as to look like claspers appended to 

 the fins. They have indeed been mistaken for these organs by 

 Prof. O. JaekelJ, who has published a restored sketch of the 

 fish, which is now unfortunately being copied in text-books. We 

 have been able to make a microscope-section of a fragment of the 

 fossilised tissue in the specimen in question, and both Dr. Dean 

 and I are satisfied that it is kidnev, not cartilage. There is no 

 trace of a pelvic clasper in any Cladoselacliid ue have examined 

 (we have seen nearly all the known specimens), and the only 

 well-preserved pelvic fins end behind in a tapering menbrane. 



Prof. Jaekel's restored sketch just mentioned also erubodies a 

 theoretical interpretation of the pectoral fins, which still needs 

 more evidence befoi'e it can be established. Apart from a few 

 parallel bars, the supports of the pectoral fin within the body-wall 

 have not hitherto been clearly seen in the specimens of Cladoselache 

 from Ohio ; but in one fragment of an obviously similar shark 

 from the Lower Carboniferous of Scotland, descrihed by Traqu:iir§, 

 the row of bars supporting the pectoral fin is continued backwards 



* Loc. cit. (1909), p, 233. 

 t Loc. clt. (1909), p. 231, text-figs. 30, 31. 



\ Sitzimgsb. k. preuss. Akad. Wiss., phys.-math. CI. 1009, p. 715, fig. 0. 

 § Cladodits neihoni, R. H. Traquair, Trans. Gcol. Soc. Glasgow, vol. xi. 

 (1897), p. 41, pi. 4. 



