FOSSIL PISHES. 23 



etc., and these as corresponding to the so-called " radius." Commentino- 

 on this interpretation, Mr. Parker says : 



" Professor Huxley, in his invaluable ' Memoir on the Ganoids,' pp. 

 34, 36, speaks of the interclavicle as ' the so-called radius ' (p. 35, Fig. 

 21, d), but it has nothing to do with Professor Owen's ' radius,' which is, 

 in reality, the coracoid." 



Here there is evidently a little confusion, for Mr. Parker elsewhere 

 (Monograph, p. 29, near bottom) says : " The large bones below are best 

 seen in Pig. 21, p. 35 (Huxley's Memoir), where c is the huge interclavi- 

 cle ; " whereas Prof. Huxley, on the page quoted above, compares the 

 antero-lateral piece (interclavicle of Parker) with the " coracoid," and the 

 poster o-lstteml piece with the so-called " radius." With this " coracoid " 

 and "radius" matter we have, however, nothing to do further than to 

 ascertain accurately Professor Huxley's view on the comparison of the 

 ventral shields of Coccosteus and Lorioaria, and to discover in wliac 

 points Mr. Parker dissents from that view. The facts seem to be as fol- 

 lows : Professor Huxley compares the median plate of the shield of Coc- 

 costeus with the urohyal of Loricaria, the anterior paired plates of the 

 shield of one with those of the other, and the posterior with the poste- 

 rior. Mr. Parker, however, regards the anterior pair of the ventral 

 plates of Coccosteus as the equivalents of the posterior pair of Loricaria, 

 and both these as interclavicles ; the anterior pair in the Siluroids being 

 supposed by him to be clavicles. 



To these conclusions I hesitate to subscribe, because if there is any 

 homology between the ventral shields of Coccosteus and Dlnichthys, and 

 those of our living Siluroids — and this is rendered highly probable, both 

 by the resemblances which they present and by the very evident homolo- 

 gies pointed out by Professor Huxley in the dorsal and cranial plates — 

 the posterior pair of plates are, anatomically, the same in both groups. 



This is indicated by their like position and backward reach, and by the 

 peculiar processes which form the posterior lateral angles in each. 



The position of these plates, as remarked by Professor Huxley, seems to 

 be so far backward as to render it improbable that they had any connec- 

 tion with the pectoral fins, and I venture to suggest that they were post- 

 umbilical and held the same position as the third pair of plates in the 

 plastron of Chelonians; and further that they represent the palmated 

 "interspinous" bones of C(Blacanthus, and like them served as supports 

 to the abdominal fins. 



Hthis is true, they belong rather to the pelvic, than to the pectoral 

 arches, and by their size, form, and solidity, were prophetic of the more 

 complete condition of the pelvic arch which characterizes the highpr 

 classes of Vertebrates. 



