184/.] LYELL ON THE COAL-FIELD OF EASTERN VIRGINIA. 277 



head are covered with extremely minute scales. 2iidly, The raylets 

 on the anterior margin of the caudal fin alluded to in Mr. Redfield's 

 description are stronger and broader in the lower lobe of the tail than 

 in the upper. 3rdly, The insertion of the anterior ray of the dorsal 

 fin begins nearly opposite the middle of the anal fin, and in conse- 

 quence of the great extension of the latter towards the tail, it con- 

 tinues to be opposite the whole length of the dorsal. The pectoral 

 and ventral fins are rarely to be seen, but have left impressions in 

 some specimens. 



Second species of the genus Dictyopyge. 



Portions apparently belonging to a second species of the same 

 genus occur in some of the slabs of stone from Chesterfield county, 

 the scales being so much larger in proportion to the size of the indi- 

 vidual, that in corresponding parts of the body, five scales occupy the 

 place of seven in the preceding species. 



Tetragonolepis. 



PI. IX. fig. 2. represents nearly the whole side, with part of the lateral 

 line near the head, of a specimen from Blackheath : natural size. 



Although a few fragments only of this ichthyolite were obtained, 

 they were recognized at once by M. Agassiz as belonging to the 

 distinct genus Tetragonolepis, and to resemble the large liassic species 

 with smooth scales. A scale from the lateral line, magnified about 

 four times («, fig. 2. PI. IX.), shows the manner in which the tube in 

 some of these scales opens outwards. Each scale in the lateral line 

 has also a notch posteriorly. 



I have stated that all the fish of the red sandstone of Connecticut 

 differ from those of Virginia. A fine collection of the former was 

 made by Prof. B. Silliman, jun., and myself, at Durham, Connecticut, 

 in 1842, which M. Agassiz and Sir P. Egerton have examined for 

 me. They belong to three species : — 1st, Palceoniscus fultus, Agassiz 

 {Ischypterus fultus, Egerton), of various sizes and ages, some of the 

 varieties comprising the Palceoniscus macropterus of Redfield, which 

 is considered by M. Agassiz to be the same. Sir P. Egerton has 

 proposed for Palseoniscus the generic name of Ischypterus, from 

 L(T)(ys, strength, and itrepov, Jin, from the great size and strength of 

 the fulcral rays of the dorsal fin. They differ from Palseoniscus, as 

 Mr. Redfield first pointed out, by having the vertebral column pro- 

 longed to a more limited extent into the upper lobe of the tail, or, in 

 the language of M. Agassiz, they are less heterocercal. The teeth 

 also, according to Sir P. Egerton, who in 1844 examined for me a 

 fine series of specimens from Durham, Connecticut, differ from those 

 of Palseoniscus in being strong and conical. The oral aperture is 

 smaller and the scales smoother than in the Palseonisci of the mag- 

 nesian limestone or Permian beds of Europe, in which the scales are 

 striated and serrated on the posterior margins. Some of the car- 

 boniferous Palseonisci of Europe resemble the American fish in having 

 similar smooth scales. 



2ndly, Catopterus gracilis. 



