and Systematic Position o/'Clielrolepis. 243 



with the clavicle. This bone is seen in Pander's tab. viii. 

 fig. 2 and tab. ix. figs. 3 & 5, but also marked 4(5, the same 

 as the preceding *. Ai'ticulated with its lower extremity is 

 the clavicle (figs. 2 &"3, cl), a bone so strong that it ia con- 

 spicuous in every nodule specimen, and seems to have been 

 able to resist compression in very many cases where every 

 thing else is crushed quite flat. This clavicle is composed of 

 two parts, set at a considerable angle to each other. Of these, 

 the upper or vertical part, set on tiie side of the shoulder and 

 forming part of the hinder margin of the branchial ojjening, 

 is of a somewhat lanceolate shape, with the posterior margin 

 more convex than the anterior, and with the apex directed 

 obliquely upwards and backwards to the lower end of the 

 bone last described. A nearly vertical line divides the outer 

 surface of this part into two, the anterior of which looks rather 

 forwards into the branchial cavity. The lower part of the 

 bone, much smaller and somewhat quadrate in form, projects 

 inwards towards the ventral middle line ; between the two 

 parts, behind, is a notch from which the pectoral fin issued. 

 This bone, the clavicle, is numbered 48 in Pander's figures ; 

 but in tab. ix. figs. 3 & 5 the number is placed on the element 

 next to be described, which is not represented as distinct ; 

 and in tab. viii. fig. 2 it is also placed on a bone which is un- 

 doubtedly the operculum. The last element of the shoulder- 

 girdle articulated to the front of the lower end of the clavicle 

 is the interclavicular plate (figs. 2 & 3, ixl), a bone wdiich 

 among recent Ganoids is not found in Lejjidosteus or Amia, 

 though it occurs both in Polypterus and licipenser and also in 

 Polyodon, and in them lies, as it does here, on the so-called 

 " isthmus." It consists of a pointed plate of bone, shai-ply 

 bent on itself along a line continued forwards from the line 

 of junction of the two portions of the clavicle, when the two 

 bones are in apposition. It thus comes also to present two 

 jwrtions or aspects — the one looking upwards and outwards, 

 forming part of the gill-slit below the branchiostegal rays, 

 and the other covering the ventral surface of the isthmus. 

 Seen from below, the ventral portion of the interclavicular 

 plate is of a somewhat elongated triangular form, the apex 

 directed forwards towards the symphysis of the jaw, the short 

 posterior side articulating with the lower end of the clavicle, 

 and in close apposition to its fellow of the opposite side, by 

 about two thirds of its long internal margin, in specimens 



* There is probably an error in the lettering here, as the number 47, 

 which Pander assigns to the "scapula," does not occur on the plate 

 at all. 



