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TRANSACTIONS OF THE AMERICAN PHILOSOPHICAL SOCIETY 



Molids. — Although excessively specialized in the form of the body, the Molidse retain 

 gills on all four branchial arches instead of on three only, as in both tetraodonts and diodonts 

 (Tate Regan, 1929, p. 325); their beak is undivided as in the diodonts but in their osteology 

 they are very similar to the Tetrodontidas (Regan). Their larvae also suggest close re- 



Mola mola 



Fig. 172. Mola mola. 



lationship with the Diodontidae. Hence we may assume that they are an offshoot of the 

 common stock of the tetrodonts and diodonts. The entire osteology of Mola has been 

 figured by Cleland (1862) and Steenstrup and Liitken (1898). The skull bones of Mola 

 are remarkably spongy and delicate, since their supporting function is largely taken over 

 by the extremely thick hide, which envelopes the entire body like a coat of blubber. As 

 the examination of dried skulls reveals only a sorry mess of distorted fragments, we present 

 a figure from a dissection of a fresh specimen prepared by my colleague Mr. H. C. Raven. 



