338 Mr. C. T. Eegan on the 



are inserted close toojether and diverge distally. Of these 

 the posterior, metapterygiuni, is the longer, whilst the shorter 

 anterior one is the first baseost. Polypterus is peculiar 

 among Crossopterygii in that the metapterygium is not split 

 uj) into or followed by a series of segments, whilst the baseosts 

 are numerous and are attached to tlie distal edge of a lamina 

 which has developed between the two basal bones, and in 

 which an ossification has arisen. Nevertheless this type of 

 fin does not appear to me to justify the proposal which has 

 been made to regard the Cladistia as a distinct order. 



As to the structure of the ventral fins of the Crossopterygii, 

 in those forms in which they were non-lobate this was 

 probably as in the Chondrostei, and the modern Polypterus 

 has an arrangement similar to that which is sometimes seen 

 in Scapliirhynchus — i. e., a single basal piece supporting a 

 short series of baseosts. There is evidence, too, that the 

 supports of the obtusely lobate ventrals were very similar to 

 those of the obtusely lobate pectorals. 



The replacement of the branchiostegal rays by the develop- 

 ment of the paired gular plates is a characteristic feature of tlie 



In Eusthenopteron the same arrangement has been described by Whit- 

 eaves (Tr. K. Soc. Canada, 1888, p. 87). Before I had seen either of 

 these descriptions I had formed the opinion that the so-called " basal 

 cartilage" in the pectoral o^ Eusthenopteron tigured by Smith Woodward 

 (Vert. Paheout. p. '!'), tig. 123) was probably coraco-scapular, on account 

 of its shape and bulk, and it appears to me to bear a most suspicious 

 resemblance to the ossification named coraco-scapular bj^ Traquair in 

 Tristichojiterus and to the coraco-scapular of the recent Polypterus. The 

 so-called postaxial process would then be the downwardly projecting 

 portion of the coracoid ; otherwise it seems to me to be inexplicable, since 

 the dermal rays do not appear to extend so far, and if such a process 

 developed on the basal segment, why not on the second ? 



The alternative supposition, which is the one apparently now adopted 

 by Smith Woodward and Traquair (Geol. Mag. 1890, p. lU), is that this 

 bone is the basal segment of the axis. If this be so, then it follows that 

 in the specimens of Tristicliopterus on which Traquair's description was 

 based this large bone had not been preserved or was hidden. 



Unless we assume that Polypterus originated independently of other 

 Crossopterygii, it seems to me clear that the primitive Crossopterygian 

 must have had a pectoral in which the tirst baseost retaii:ed its attach- 

 ment to ihe coraco-scapular, for I regard the theory that the acutely 

 lobate synunetrical tin has given rise to the t)btusely lobate asymmetrical 

 tin as exploded, and 1 shall require mure i-atisfactory evidence than has yet 

 been forthcoming to convince me that this condition is not realized in 

 Tristichopterus or Eusthenoptertn, as would appear from the original 

 description of each. 



I must add that I have been in correspondence with Dr. Traquair, who 

 has very kindly told me that he is not inclined to accept my view, which 

 I put forward here merely for the purpose of stating a case. 



