1854.] EGERTON FOSSIL FISH FROM THE NEW RED. 369 



DiPTERONOTUs CYPHUS. (FroHi the Bunter of Bromsgrove.) 



Gen. char. Head diminutive ; body short and deep ; back steeply- 

 vaulted ; two dorsal fins ; tail homocerque ; scales ganoid. 



The singular featiires (not to say deformities) of this remarkable 

 fish are so striking and uncommon, that, while on the one hand they 

 designate it as a new generic form, on the other they leave it in 

 doubt to what family it belongs. Afiinities it has none with any 

 fossil fish hitherto known. It is difficult for mere words to convey 

 any idea of its peculiarities. To conceive a small Platysomus with a 

 diminutive head, and a back exalted into a dome proportionately as 

 large or larger than the hump of a Camel, with an angular fin perched 

 on its summit, and a second fin of similar form behind it, is a consi- 

 derable stretch of imagination, but yet is inadequate to portray all 

 the eccentricities of this curious fossil. Unless I am mistaken, its 

 character is still further complicated by a caudal fin, almost if not 

 quite homocercal ! and this in a fish of the age of the Bunter Sand- 

 stone ! Whether this be so or not, the peculiar characters of the 

 double dorsal fin will at once arrest the attention of ichthyologists, as 

 of unusual occurrence in the fishes of the mesozoic strata. Among 

 the earlier races of fishes of the families Saui'oidei-dipternni and 

 Goelacanthi, the occurrence of the double dorsal is the rule and not 

 the exception ; but it is generally associated with a double anal, and 

 is one of those embryonic features rendered permanent, which we 

 also recognize in the persistence of the notochord and the various 

 gradations of ossification in the vertebral elements. The Acantho- 

 deian genus Biplacanthus, it is true, exhibits two distinct dorsal fins, 

 but the fins of this family, with the exception of the abnormal genus 

 Cheirolepis, are membranous, and supported by ichthyodorulites, not 

 jointed at the base, as in the spines of all bony fishes, but plunged 

 into the integuments, as in Spinax and other Placoid genera. In 

 the remaining families of the Ganoids, there is no instance of a double 

 dorsal, as far as is yet known, in the Sauroidei and Pycnodonti ; and 

 only two small genera in the Lepidoidei, viz. Notagogus and Pro- 

 pterus, from the upper Oolites of Kelheim, in which this peculiarity 

 obtains. 



The occurrence, in an older deposit than the Lias, of a Ganoid fish 

 having a homocerque tail, forms an exception to the ordinary rule 

 founded by Agassiz as the result of his past experience in the study 

 of fossil ichthyology. One single instance came under his notice of 

 a heterocerque genus above the Lias, but no case of a homocerque fish 

 beneath that formation. The remarkable genus Borypterus, found 

 in the Kupfer-Schiefer of Mansfeld, is described by Prof. Germar 

 as having a homocerque tail, but there is some doubt of the fact from 

 the imperfect condition of the only specimen he had examined. 



Description. — This fish measures 3 inches in length from the 

 point of the nose to the fork of the tail, and l|- inch in depth from 

 the base of the anterior dorsal fin to the insertion of the ventral fin. 

 The head is very diminutive, and measures only f of an inch in 

 length by f in depth. It projects in a remarkable manner from 



