Bliss.] 386 [Februarys, 



February 3, 1875. 

 The President in the chair. Twenty-six persons present. 



Mr. Richard Bliss, Jr., described some peculiarities in the 

 structure of the fin spines of certain groups of fishes. 



The spines of the dorsal and pectoral fins of the Siluroids and 

 Doradoids differ from those of ordinary fishes in that they serve not 

 merely as supports for the fin membrane, but are also modified into 

 weapons of defence. In both of these families, but especially in the 

 Doradoids, the very large spines of the dorsal and pectoral fins are 

 furnished in front with a row of obtusely conical, and behind with a 

 row of recurved teeth. The peculiar structure of these spines may 

 be advantageously studied in the genus JElurichtkys, as in that genus 

 the spines do not undergo that complete ossification which in most 

 other genera renders a determination of their intimate structure 

 difficult. The spine in its early stages is simply a jointed rod, each 

 joint sending off from its upper anterior portion a pair of long, slen- 

 der and nearly erect branches, which are united and somewhat 

 broadened at their outer extremities. As the branches from one 

 joint rest closely against those of the joints above and below it, a 

 hollow space is formed, pervading the whole length of the spine. 

 This space is reduced in diameter as the spine ossifies, till finally 

 there is left only a narrow channel perforating the longitudinal axis 

 of the spine ; but it is never closed at the top, as is the case with the 

 spines of certain sharks. 



As the spine ossifies, the ends of the branches project a little 

 beyond the anterior border of the spine, and in time assume the form 

 of conical teeth. At the same time the joints develop into aduncous 

 teeth posteriorly, increasing in size as the ossification proceeds; and 

 finally, with the soldering together of the branches and the oblitera- 

 tion of the joints, we have a bony spine apparently homogeneous 

 in structure, furnished with strongly serrated anterior or posterior 

 edges. 



In this peculiar structure the spines of the Siluroids differ entirely 

 from those of other Ganoids; as in the sturgeon, the spines are com- 

 posed of a number of simple rods soldered together, while in the 

 Lepidosteus, the spines along the upper portion of the caudal fin 

 are merely modifications of the plates of the body, elongated and 

 narrowed to serve a special purpose. 



