Cope.J 57o [March 7, 



In 1871* the writer gave the following as the primary divisions of the sub- 

 class Pisces : Holocephali, Selachi, Dipnoi, Crossopterygia, Actinopteri. 

 The Holocephali was raised to an equivalency with the other sub-classes 

 on account of the absence of distinct hyomandibular bone. The Dipnoi 

 were defined by the median pelvic element, by the distichous arrangement 

 of the segments of the pectoral and ventral fins, when present, on a me- 

 dian axis, and by the supposed presence of a distinct hyomandibular bone. 

 The latter definition must be abandoned, for though an ossification exists, 

 it has been shown by Stannius, Huxley and Gtinther, to be merely a de- 

 posit in the continuous chondrocranium. The sub-class Crossopterygia 

 ■was substituted for the sub-class Ganoidea of Agassiz and Miiller, as the 

 latter was believed to have no actual existence as a division of fishes. After 

 comparing the osteology of Polypterus, Lepidosteus and Amia, I remark 

 (p. 320) " It is thus evident that the sub-class Ganoidea cannot be main- 

 tained. It cannot be even regarded as an order, since I will show that 

 Lepidosteus, Accipenser, and Amia, are all representatives of distinct orders. 

 I hope, also, to make it evident that Polypterus should be elevated to the 

 rank of a sub-class or division of equal rank with the rest of the fishes and 

 with the Dipnoi, already adopted." The sub-class Ganoidea has not yet 

 fallen into disuse, but there are strong symptoms that it will do so.f 

 Among others I select the following extract from Huxley's paper on the 

 ovaries of the smelt, published in 18834 



"As is well known, Lepidosteus presents an example of a Ganoid with 

 oviducts like those of the higher Teleostei ; in Osmerus, on the other 

 hand, we have a Teleostean with oviducts like those of the ordinary 

 Ganoidei. It is tolerably obvious, therefore, that the characters of the 

 female reproductive organs can lend no support to any attempt to draw 

 a sharp line of demarkation between the Ganoids and the Teleos- 

 teans. 



"Boas has recently conclusively shown that the same is true of the sup- 

 posed distinctive character afforded by the conus arteriosus ; and it has 

 long been admitted that the spiral valve which has been described in the 

 intestine of Chirocentrus is the homologue of that which exists in all the 

 Ganoids, though greatly reduced in Lepidosteus. Indeed I am inclined to 

 believe that the circular valve which separates the colon from the rectum 

 in the smelt is merely a last remainder of the spiral valve. Thus, among 

 the supposed absolute distinctions between the Ganoids and the Teleostei, 

 only the peculiarities of the brain, and especially the so-called chiasma of 

 the optic nerves, remain for consideration. My 'lamented friend Mr. 

 Balfour, in the last of his many valuable labors, proved conclusively that 

 the brain of Lepidosteus is, both in structure and development, a Teleostean 



* Proceedings Amer. Assoc. A.dv. Science, p. 326. Transac. Amer. Philosoph. 

 Soc, p. 449. 



t The term ganoid can be used as an adjective to describe the scales already 

 known by that name, and thus be preserved. 



% Proceedings Zoological Society of London, 1883, pp. 137, 138, 139. 



