1853.] EGERTON — 'PALICHTHYOLOGIC NOTES. 277 



It may not be out of place here, to consider shortly the bearmg of 

 the foregoing remarks upon the general arrangement of this farnil3^ 

 The position assigned by Prof. Agassi z to the genera Tetragonolepis 

 and Bapedius was mainly owing to the proximity of the flat-bodied 

 genus Platysomus, at the brink of the heterocerque ganoids ; but the 

 removal of the latter genus to the Pycnodont family breaks up this 

 link of affinity at the commencement of the family, to add it at the 

 close. Moreover, the discovery of the American genera Cato2)tetnis 

 and Dictyopyge, the former a heterocerque, the latter a homocerque 

 form, renders the transition from the genus Palceoniscus to Pholido- 

 phorus, perhaps the two most typical representatives of their respect- 

 ive families, both gradual and natural. Taking then Pholidophorus 

 as the starting-point, we find the affinities of the other genera assuming- 

 two diverging lines, the one passing by Nothosomus, Notagogus, and 

 Ophiopsis to the Sauroid, the other by Lepidotus, Semionotus, Am- 

 blyurus, Dapedius, and Tetragonolepis to the Pycnodont family. 



Since the foregoing communication was forwarded to the Geological 

 Society, I have fortunately found a specimen in the British Museum, 

 which furnishes the only link wanting in the evidence to substantiate 

 the genus Tetragonolepis as a member of the Pycnodont family. 

 This is a large and undescribed species from the lias of Boll, having 

 not only the dermal characters above alluded to, clearly, distinctly, 

 and most unmistakeably displayed, but showing also the character of 

 the dentition. In this respect it has a very close resemblance to the 

 genus Microdon, but the masticatory apparatus is even smaller in 

 proportion to the size of the fish than it is in that genus. 



Description of Species. 

 Family PycnodontidyE, Agassiz. 

 Genus Tetragonolepis, Bronn. 



1. T. SEMiciNCTUs. Described by Prof. Bronn in the 'Jahrbuch 

 fiir Mineralogie,' &c. 1830, p. 22 : ' Poissons Fossiles,' vol. ii. p. 196, 

 pi. 22. figs. 2 & 3. 



Locality. Lias of Neidingen. 



2. T. SUBSERRATUS, Miinster. Described by Count Miinster in the 

 'Jahrbuch fiir Mineralogie,' &c. 1842, p. 97. I am very much in- 

 clined to believe that this species is identical with the former. The 

 only character assigned by Count Miinster for its specific distinction, 

 is the serration of the carinated series of scales on the abdomen. This, 

 however, appears to be constant in all the species of the genus I have 

 seen, and may, for anything Bronn states to the contrary, obtain also 

 in Count Althaus' specimen. Indeed he describes the simple series 

 of projecting ventral scales as reminding him of the appearance of the 

 " dentelure abdominale" in the genns Pristigaster. This seems a 

 common fish in the lias strata of Banz and Boll. There are specimens 



