70 M. E. Storms on the Adhesive Dish o/Echeneis. 



of the latter being opposite to wliat it is in other fislios, the 

 lower extremities of the intern eurals pointing backwards 

 instead of forwards. The upper expanded portions of the 

 interneural spine each carry a pair of lamellae at their junction. 



/8. Intercalary hone. — This is a lamellar bone formed of 

 wing-like plates, with a narrow connecting part whicli expands 

 in its middle and rests partly on the interneural spines. The 

 wing-like anterior parts of the consecutive intercalary bones 

 overlap one another, like the tiles of a roof. 



y. Pectinated lamelJoe. — These are paired bones, joining 

 two by two in the median line and occupying the v/hole sur- 

 face of the disk. They have an elongated shape. Their 

 posterior margin carries the bands of small teeth mentioned 

 above. One of these teeth, placed at the junction of the two 

 lamella3, is much longer than the others and is situated on a 

 lower plane. It has a curved shape, and suggests the idea 

 of a spinous ray ; but it does not form a continuous part of 

 the pectinated lamellas. Each lamella carries at its anterior 

 margin, nearer to the median line, a strong process. It is 

 directed forwards and passes downwards through the inter- 

 spaces left between the intercalary bones. 



B, The anterior extremity of the disk ends in a segment 

 rounded anteriorly and formed by the fusion of the different 

 kinds of elements already mentioned — the pectinated lamellse, 

 an intercalary and an interneural spine. Although it is dif- 

 ficult to make out all the bones which enter into the com- 

 position of the anterior extremity of this segment, it is 

 curious to remark the presence of a small spine which appears 

 to represent the longest of the small teeth, all the others being 

 quite absent. 



C. The ])osterior extremity finishes by a notch partly con- 

 taining a curious round ossification, which may possibly be a 

 modified interneural. 



II. Description of a normal Spinous Dorsal Fin. 



We shall take the spinous dorsal of Scomber ^ as this fish 

 belongs to the same division as Echeneis. 

 Here we also find three elements : — 



1. The interneural spine; 



2. An intercalary bone ; 



3. A spinous ray. 



1. The interneural spine {axonost of E. D. Cope^ and 

 Ryder) may be divided into two parts : — 



* E. Cope, ' American JX at lira list,' vul. xxi. ku. 11, 1887, p, 1015, 



