550 PROF. T. W. BRIDGE ON THE MESIAL 



SALMOlflPiE. 



Coregonus poUan. 



Dorsal fin. — In the rayed dorsal fin there are twelve radial 

 elements, supporting thirteen fin-rays. Of the radial elements', 

 six, viz. the sixth to the eleventh inclusive, are trisegmental. The 

 suture between the mesial and proximal segments is occasionally 

 somewhat diflBcult to detect, but sections taken through the line 

 of junction readily prove its existence. The first two elements 

 and the last consist of proximal segments only, and the third, 

 fourth, and fifth of a distal segment in addition. 



The first radial element supports two fin-rays, of which the 

 second rightly belongs to that element. All the remaining 

 elements are each related to a single ray, although, as in the 

 preceding Teleosts, two elements contribute, directly or indirectly, 

 to the support of each. 



A series of fifteen slender bones is situated in front of the first 

 of the ray-bearing radial elements, imbedded in the median 

 fibrous sheet separating the dorso-lateral muscles of opposite 

 sides of the body, and agreeing in number with the subjacent 

 vertebrae. Anteriorly to these, and continuing the series to the 

 posterior face of the skull, there are two thin lamelUform bony 

 plates, of which the anterior is much the larger. The seventeen 

 slender or lamelliform ossicles are the proximal elements of a 

 series of vestigial radial elements, and may be taken as an indi- 

 cation of a primitive extension of the dorsal fin as far forwards 

 as the head. 



Anal fin. — Eleven radial elements and thirteen fin-rays are 

 present. The third to the eleventh of the radial series inclusive 

 are trisegmental, the first and last unisegmental, and the second 

 bisegmental. 



The third fin-ray is the one belonging to the first radial 

 element, which therefore supports two rays in addition to its 

 own proper ray. 



SlLTTBID^. 



JPlaty stoma tlgrinum. 

 Dorsal fin. — With the exception of certain minor differences, the 

 dorsal fin of this Siluroid resembles that of Amiurus catus which 

 has been described by McMurrich [9]. There are eight distinct 

 radial elements and a corresponding number of fin-rays (PI. XXI. 

 fig. 14). The five posterior radial elements are fairly similar, 



