25° 



HARD WICKE ' 6" S CIENCE - G O SSIP. 



Dipienis is also closely related to that of Ceratodus, 

 as well as Lepidosiren. 



Thus the history of the Dipnoi, an order before the 

 discovery of the Australian Ceratodus only represented 

 by the mud-fishes of Africa and South America, is 

 carried back to remote geological ages, and the four 

 living representatives at present known are found to 

 be the survivors of a well-defined and characteristic 

 group of fishes first appearing in the Devonian age. 

 They can be traced up from Diptenis, through the 

 Carboniferous Ctenodits, to the Jurassic Ceratodonts, 

 and then the link is lost sight of until their lineal 

 descendants reappear widely distributed on the surface 

 of the present world. This is but an illustration of the 

 truth that species which have the greatest vertical range 

 in time have also the widest geographical distribution, 

 or that a wide distribution proves the antiquity of the 

 genus. It is certainly a very significant fact that the 

 group of living fish most closely allied to the amphibian 

 reptiles should be represented in the Devonian rocks 

 long before the most simply constructed amphibians 

 appeared on the scene of life in the swamps of the 

 Carboniferous period. The Dipnoi, as at present 

 constituted, comprise the following families : Pro- 

 topterina, Ceratodontijia, Ctciiododiptendiv, and possibly 

 Phaneropleurida. They are closely allied to the 

 Ganoids, and especially to that sub-order termed by 

 Prof. Huxley the Crossoptcrygida, or "fringe-finned," 

 to be presently referred to. Dr. Giinther, indeed, pro- 

 poses to unite the Dipnoids with the Ganoids, as a 

 distinct family ; but Prof. Huxley considers that, 

 though nearly related to that order, they yet possess 

 many important differences. It seems as if the 

 Dipnoihoid also some affinities with the group of fishes 

 known as Placoderms, for a most remarkable fossil 

 fish has recently been discovered in America, the 

 dentition of which is almost exactly like that of 

 Lipidosiren, except that it is about one hundred times 

 greater. The genus Dinichthys was founded by Prof. 

 Newberry for the reception of this gigantic Placodcrni, 

 of which two species at least are recognized and 

 graphically described by him in vol. ii. of the State 

 Reports of the Palaeontology of Ohio. They occur 

 in the Huron Shales of the Upper Devonian series, 

 where they seem to have preponderated in number, 

 fragments of over a hundred individuals having been 

 detected, while the remains of other genera are found 

 more rarely in the same horizon. The original speci- 

 mens of D. Terrelli were destroyed by fire, but 

 fortunately a'photograph had been secured, from which 

 the plates exhibited were taken. The jaws of this 

 "terrible fish" were each two feet long, the breadth 

 of the head was about three feet, and the cranium was 

 composed of massive bony plates, the solid bone of 

 the occipital portion being three inches in thickness. 

 The length of the body is estimated liy Prof. Newberry 

 to have been about fifteen feet, and its diameter three. 

 The anterior was protected liy huge dorsal and ventral 

 shields, resembling, in general shape and structure. 



those of the genus Coccosteiis, rendered classic by the 

 pen of the lamented Hugh Miller. Very little is 

 known with regard to the fins, " about six inches only 

 of an apparently median fin, with well ossified rays 

 as thick as one's little finger," having as yet been 

 found, and, from the absence of scales, it is conjectured 

 that the posterior portion of the body of the animal 

 was covered %\'ith a tough skin, as in Coccosteiis, a 

 genus which possibly protected itself, like the modem 

 sheat-fish of the Ganges, by burrowing in the mud, 

 watching for prey with only its mail-clad parts exposed. 

 The powerful dentition of Dinichthys is suggestive of 

 carnivorous habits, and probably, being so heavily 

 weighted by the thick shields encasing its vital organs, 

 it would be compelled to obtain food rather by cunning 

 than by swift pursuit. It is worthy of notice that 

 the ponderously armed Placoderins'ha.6. a comparatively 

 short range in time, remains of the group being only 

 found in the Silurian and Devonian rocks : thus it 

 seems as though, unable to cope in the struggle for 

 existence with the lighter armed and more active race 

 of ganoids which predominated in the Devonian 

 waters, they died out, leaving no immediate 

 descendants. The vertebral column in the Placoderms 

 was generally cartilaginous, a condition considered by 

 some authors as indicative of a low organization ; but 

 as the quantity of bone composing their external 

 shields was much greater than that forming the 

 internal skeleton of the existing types of true bony 

 fishes, and as traces of ossified caudal vertebrise have 

 been discovered in one genus, they ought rather to be 

 highly placed in a systematic classification. The 

 group is considered by Professor Huxley to form a 

 link between the Ganoids and the Teleosts, and as 

 having most affinity with the living plated Siluroid 

 Teleosts of the African rivers. 



( To be continued. ) 



NOTES ON MARINE AQUARIA. 



AS there were two communications in a recent 

 number of Scien'CE-Gossip, relative to fresh- 

 water aquaria, perhaps a few notes concerning the 

 keeping of marine life Avill not be uninteresting. I 

 have three tanks, made of wood, with plate glass 

 fronts, the two larger of which have a false bottom of 

 slate sloping from the front up to the back, and 

 which are so made in order to obtain a varying depth 

 of water. These contain respectively thirteen and 

 nine gallons, and to efficiently aerate such a body of 

 water, I have connected a double-acting pair ot 

 bellows with a jDipe running along the bottom, and 

 which is pierced at intervals with very small holes. 

 The pipe most suitable for the purpose is that ordi- 

 narily used by gas-fitters, and known as " composition 

 pipe," but lest the salt water should act upon the 

 metal and prove injurious, it is advisable to varnish 

 the inside with a solution of shellac in spirits of wine. 

 This I did thoroughly, in addition to coverhig the 

 outside with pitch, in fact, the whole of the interior of 



