SKELETON OP REGALECUS ARGENTEUS. 19 



intersegmental) elements, is probably intersegmental, and should thei-efore retain its 

 usual name of basihyal. 



It will probably be urged against the above view, that in the Salmon and other 

 Teleosts which have been carefully examined, the so-called basibranchials are ossifi- 

 cations in a continuous cartilage, what I have called the true basibranchials being 

 mere synchondroses : and further, that one can hardly expect a primitive mode of 

 segmentation in a highly specialized Acanthopterygian like Regalecus. But it must 

 be borne in mind that the skeletons of Teleosts are, more often than not, examined dry, 

 in which condition there would be no distinction between a distinct intercalated 

 cartilage and a synchondrosis. Moreover, as we know practically nothing about the 

 phylogeny of the various Teleostean groups, it is certainly premature to say that 

 " primitive " arrangements should or should not be found in any one of them. 



Attached to the branchial arches are the delicate parosteal gill-rakers, of which each 

 of the first four arches bears two sets, an anterior {a.g.r), and an internal (i-gr). 

 In the second, third, and fourth arches, each series consists mainly of delicate 

 triangular laminae, about ^o i'^^h in length, set transversely to the long axis of the 

 arch. Alternating with these, which may be called i)rimary ossicles come smaller 

 secondary ossicles, not more than ^ inch in length, and between these and the primary 

 are intercalated a tertiary set, less than ^ inch high. Calling the primary ossicles 

 A, the secondary B, and the tertiary c, their typical arrangement on the branchial 

 arches is shown diagrammatically thus : — 



AcBcAcBcA. 



On the first arch, the primary ossicles of the anterior series (a.g.r^) are greatly 

 elongated, forming scythe-like laminae a little more than an inch in length. Those on 

 the cerato- and upper part of the hypobranchial are kept in place by a fold of 

 pigmented mucous membrane about ^ inch wide, which unites their proximal ends: 

 the secondary and tertiary ossicles are attached to the free border of this membrane, 

 being thus carried quite away from the branchial arch itself. 



In the fifth arch only, the internal series of ossicles is present. On the first arch 

 both series are continued on to the pharyngo-branchial : in the remaining arches this 

 is not the case, but the pharyngo-branchials are fringed with delicate spinose denticles. 

 Similar denticles fringe the edges of all the gill-rakers. 



6. The Veetebkal Column and the Doesal Fin. 

 (Plate III. fig. 5, and Plate VI. figs. 20-26.) 

 The vertebral column consists of 93 vertebrae, with the neural arches of which are 

 connected 206 interspinous bones, serving for the attachment of 205 (15 + 190) dermal 

 fin-rays. 



d2 



