EXPLANATION OF PLATE Vm. 



Fig. 1. Youngest stage of development referred to ifola, and known as Ostradon loops 

 (from a drawing by Sir J. D. Hooker, published by Richardson), supposed 

 to be enlarged. 



Fig. 2. Molacanihus stage of Mola. From Gunther. 



Fig. 3. Molacanihus at&gQ of Mola. SlightlyalteredfromaMS. figure by F.W.Putnam. 



Fig. 3a. Caudal vrrtebrfe of Molacanthua, together with their spines and musculature 

 exposed, showing rudimentary rays and what seem to be traces of caudal 

 interspinous elements, drawn from a specimen in the U. S. National Museum, 

 somewhat enlarged. 



Fig. 4. A young specimen of Mola some time after it has passed the Molacanthm con- 

 dition, with the dermal spines still in place. (A spine which is found just 

 below the pectoral seems not to be represented.) From Gunther. 



Fig. 5. A young Mola, showing the scars where the dermal spines of the Molacanthua 

 stage have dropped oflf, and with the median ray-bearing projection from 

 the center of the caudal represented. (The caudal has been represented as 

 somewhat wider than in the alcoholic specimens, which seem to have been 

 somewhat shrunken.) From specimens in the U. S. National Museum. 



Fig. 6. Median caudal projection of a somewhat older specimen than the preceding, 

 showing the rays to be composed of fused horny fibers at this time. 



Fig. 7. A diagram intended to show the parts which have been lost in the caudal 

 skeleton of Mola. The black interspinous elements are supposed to be 

 swong forward against the neural and haemal spines of the sixteenth verte- 

 brae. The end of the chorda in dotted outline, and the shaded interspinous 

 jjieces, with their correspondingsegments, are supposed to have been aborted. 



Fig. 8. Caudal skeleton and part of the muscles of the young of Mola in the condition 

 of Fig. 5, somewhat altered from a MS. figure by F. W. Putnam, in order 

 to show the dichotomous caudal rays, which seem to become partially 

 aborted in the central portion as the animal becomes adult, and to undergo 

 other retrogressive changes. 



Fig. 9. A reduced figure of the caudal skeleton of an adult of Mola rotunda, which 

 shows that the median interspinous elements become coossified, while the 

 ends of the rays become hidden or more thickly covered by the integument. 

 This figure illustrates the most extremely modified example of the gephy- 

 rocercal tail. From Wellenbergh. 



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