Bashford Dean rally, 
of “inter-clavicular” or “claviculoid” membrane bones in certain 
genera, but that the basal region of a fin may be strengthened with many 
dermal elements. This is well shown in a specimen of Parexus falcatus 
in the British Museum, P. 130 (Fig. 21), of which an enlarged figure of 
the base of a pectoral fin is shown in the present Fig. 27; here as many 
as half a dozen dermal elements may be counted along the mesial margin 
of the basal plate, and it is even possible that the entire flat distal surface 
of this plate was strengthened by dermal elements. Accordingly, the 
shoulder girdle of Acanthodians, like the girdle of a teleost (siluroid, 
for example) is to be treated as including a dermal complex. Our pres- 
ent knowledge does not warrant us in attempting to homologize its ele- 
ments with those in the higher forms (as, nevertheless, Jaekel has done 
in identifying “suprascapular,” “scapular,” “coracoid,’ and “ clei- 
thral” elements), since such structures can only be compared with the 
conditions in the higher vertebrates when it has been shown that the 
Acanthodians have closer phyletic relationships to the higher forms. 
Until this can be demonstrated the structural elements of the Acantho- 
dians must evidently be interpreted in terms of their nearest kindred; 
v. e., fossil and recent sharks. The safest conclusions in our present 
stage of knowledge are, I believe, these: That we are to regard the 
proximal portion of the shoulder girdle, the region of sg in Figs. 18, 
19, 21 (elements a, b, c, of Jaekel) as equivalent to the proximal portion 
of the shoulder girdle in sharks; the distal portion becomes a region 
of concentrated fin-supporting elements, fused basals, a portion of the 
basal parts of the radials, with as an important if not a maximum com- 
ponent a dermal complex, e. g., the region d in Fig. 19 or the more 
discrete elements in Fig. 27. With regard to the homology of the 
cartilaginous pieces which Jaekel and Reis describe in A. bronnt, as fin- 
web-supporting elements placed immediately behind the pectoral spine, 
one may, I conclude, regard them as the remains of the series of baso- 
radial elements. ‘The elements of this series had in general, as has been 
noted, fused at the base of the pectoral fin spine; but it is by no means 
improbable that in certain forms a number of the posterior elements 
remained discrete, retaining more or less accurately their primitive func- 
tion. That there is the greatest range in the degree of concentration 
of fin-suporting structures in the Acanthodians all will, I think, agree 
who have examined these structures in many genera. 
The supports of the ventral fins, so important in the general discussion 
of the origin of the paired limbs, have, as far as I am aware, never been 
described. Interesting, accordingly, is the specimen of Diplacanthus 
