4 FOSSIL FISHES OF THE ENGLISH CHALK. 



larger than the latter ; dorsal fin much elevated and extending along nearly the 

 whole of the back, with two to fonr very short and rather stont anterior spines ; 

 anal fin compai'atively low, opposed to the hinder half of the dorsal, with three to 

 five short and stout anterior spines ; caudal fin deeply forked. Scales thin and 

 small, except a series of ventral ridge-scales on the short abdominal region. 



Type Specirs. — AipirJith//s prrfiosns (Steindachner, Sitzungsb. k. Akad. Wiss., 

 math.-naturw. CI., vol. xxxviii, 1859, p. 763, pi. i, fig. 1) from the Cretaceous 

 (supposed Urgonian) of Comen, Istria. 



Remarks. — This is the highest type of fish to which any specimen hitherto 

 discovered in the English Chalk can be referred. The genus comprises small 

 species, none more than 10 cm. in length, which are known by nearly complete 

 skeletons crushed between the laminse of the fissile Cretaceous limestones of Comen 

 (Istria), the Isle of Lesina (Dalmatia), and Hakel (Mt. Lebanon). The specimens 

 from Hakel were for many years ascribed to the allied genus Plata,r, which survives 

 in existing seas. The accompanying restoration (Text-fig. 1) of the skeleton of 

 Aipiclifhys relifpr, however, shoAVS that the fish differs from Platax in having a 

 larger mouth, a much less elevated anal fin, and a deeply forked caudal fin. The 

 thickened ventral ridge-scales also distinguish the Cretaceous from the Tertiary and 

 Recent genus. 



1. Aipichthys nuchalis (Dixon). 



1850. Microdon michalis, F. Dixon, Geol. Sussex, p. 369, pi. xxxii, fig. 7. 



1887. Platax (?) nuchalis, A. S. Woodward, Auu. Mag. Nat. Hist. [5], vol. xx, p. 342. 



1901. Aipichthys nuchalis, A. S. "Woodward, Catal. Foss. Fishes B. M., pt. iv, p. 429. 



Tijpa. — Imperfect fish, probably from zone of Holasfer suhylohosus ; British 

 Museum. 



Specific Characters. — Not yet satisfactorily ascertained. 



Description of Specimen. — This species is still known only l)y the unique type 

 specimen, Avhich is too incomplete to decide more than its generic relationships. 

 Dixon's drawing of the fossil does not exhibit many of its essential features, but a 

 study of the actual specimen reveals some of them. The supraoccipital bone of 

 the cranium is shown to be raised into a large, laterally compressed, triangular 

 crest. The vertebral centra, with their arches, are well ossified, and there seem to 

 be only ten in the abdominal region. Of the pectoral fins no fragments remain, 

 but each of the pelvic fins is represented by a single robust spine, though there are 

 no traces of the articulated rays. Evidence of a much-elevated dorsal fin is seen in 

 a series of large, wide-winged fin-supports above the vertebral column, just behind 

 the supraoccipital crest. The anal fin is represented by its three small anterior 

 spines. The total length of the fish cannot have exceeded 8 cm. 



