THE STATE GEOLOGIST. 47 



tically unchanged from the Silurian down to the present day. 

 This is the great subclass of cartilaginous fishes, or Elasmo- 

 branchs ( chimasroids, sharks and rays), by many supposed to be 

 the ancestral stem from which all modern fishes have been derived, 

 or at least which may be looked upon as representing most nearly 

 the persistent ancestral condition of fishes. Amongst the salient 

 characteristics of Elasmobranchs, by which they may be distin- 

 guished at once from all modern fishes, are to' be noted ( 1 ) their 

 cartilaginous skeleton; (2) shagreen integument; (3) heterocer- 

 cal (asymmetrical) tail; (4) separate, slit-like gill-openings, 

 metamerally arranged; (5) clasping organs in the male, and (6) 

 various internal peculiarities. The skeleton is cartilaginous, 

 sometimes calcified to a considerable extent, but never ossified, 

 and never with dermal bones. The sturgeon is one of the few 

 existing fishes which also has a cartilaginous skeleton and het- 

 erocercal tail — that is to say, one with a much produced superior 

 lobe, instead of having the upper and lower lobes about equal; 

 but it differs in its remaining characters, such as the absence of 

 shagreen, of slit-like gills, presence of dermal bones, etc. Even 

 a superficial examination of any shark or ray must serve to con- 

 vince one that the characters enumerated above, taken in their 

 entirety, are very trenchant, but there are numerous others besides 

 these. For very full and minute accounts of the structure and 

 habits of Elasmobranchs, it will be necessary to' consult standard 

 works on ichthyology, such as Dr. Gunther's "Introduction to the 

 Study of Fishes," the volume on Fishes in the "Cambridge Nat- 

 ural History," or Bashford Dean's "Fishes, Living and Fossil." 

 The following general remarks, taken from the second of the 

 works just mentioned, must suffice for the present discussion. 



"The Elasmobranchs are for the most part active predaceous 

 fishes, living at different depths in the sea, from the surface to 

 nearly a thousand fathoms, and ranging from mid-ocean to i the 

 shallower waters round the coasts in almost every part of the 

 world. Although typically marine, they sometimes ascend rivers 

 beyond the reach of tides, and a few are permanent inhabitants 

 of fresh water. They are most abundant in tropical and sub- 

 tropical areas, where they also attain their greatest size, and are 

 numerous in temperate regions, but there are some species which 



