32 BULLETIN OF THE 



acters by the ndnlt of the recent form that belong to the embryonic of 

 the lowest of the other recent sharks. 



Whether Chlamydoselachus gives a fair idea of the shapes of the De- 

 vonian Galei is a question we may not be able to answer satisfactorily 

 at present. The genus bears evidence of having been considerably modi- 

 fied in more recent times. But, being of lower rank through possession 

 of characters comparatively more or less embr}'onic, it affords us a safer 

 starting-point for an estimate of ancestry than do the others, which have 

 in attaining higher rank experienced considerably more modification. 



Starting from the specimen, then, its less remote ancestors differed 

 from it somewhat as follows : their teeth were less slender and more stri- 

 ate, more like the scales at the angle of the mouth ; the teeth not being 

 so much hooked, their jaws and the suspensorium were shorter; their 

 branchial laminae were more free at the outer ends, — may have pro- 

 truded ; their scales in general were more like those of the flank or belly ; 

 and in them the dorsal resembled the anal in size and shape, or at an 

 earlier period both may have been confluent with the caudal. 



If we were to hazard a conjecture as to Cladodus, we should make the 

 body elongate; the mouth anterior; the jaws and suspensorium but 

 moderately long; the scales flattened and irregular in shape, but, judg- 

 ing from the teeth, to some extent possessing keels or spines ; the oper- 

 cular flap broad and free across the isthmus, as in certain larval Batrachia 

 before coalescence with the pectoral region ; the branchial apertures six 

 or more in number; the eye without a nictitating membrane ; the noto- 

 chord persistent and unconstricted ; the vertebrte imperfect or the col- 

 umn unsegmented ; the bulbus elongate and many-valved ; the pelvis a 

 broad elongate plate ; the lateral line an open groove; the dorsal large; 

 and, possibly, the tail diphycercal, the abdomen with tropeic folds. 



As we see them by the aid of Chlamydoselachus, it appears that the 

 Cladodonti of the Middle Devonian, though low in rank, were true 

 Sharks, and that the primitive form connecting them with the Fishes is 

 to be sought farther back, in the earlier Devonian or in the Silurian. 



Cambridge, July 4, 1885. 



