HOMONOTUS. 25 



Geimx HOMONOTUS, Dixon. 

 Homonotus, F. Dixoii, Geol. Sussex, 1850, p. 872. 



Gpueric Cliaracfers. — Trunk deepened and laterally compressed, with rounded 

 ventral border. Frontal region of skull not deeply ridged ; jaws with minute 

 clustered teeth ; orbit small or of moderate size ; preoperculum without spine, only 

 serrated ; operculum produced into one long spine behind. Pelvic fins, with one 

 spine and G divided rays, arising below the origin of the pectorals ; dorsal fin much 

 extended, its anterior portion comprising at least 12 long and slender spines, which 

 are not pressed closely together ; anal fin with -i large spines. Scales pectinated, 

 rather large and thin, none much enlarged or thickened ; lateral line forming a 

 conspicuous ridge. 



Type Species. — Homonotus dorsalis from the English Chalk. 



1. Homonotus dorsalis, Dixon. Plate VII, figs. 6, 7 ; Plate VIII, figs. 0, 7. 



1850. Homonotus dorsalis, P. Dixon, Geol. Sussex, p. 372, pi. xxxv, fig. 2. 



1888. Homonotus dorsalis, A. S. Woodward, Proc. Geol. Assoc, vol. x, p. 329. 



1901. Homonotus dorsalis, A. S. Woodward, Catal. Poss. Fishes B. M , pt. iv, p. 408. 



Ti/pf. — Imperfect fish from Mailing, Sussex ; Willett Collection, Brighton 

 Museum. 



Specijie Cluiraders. — The type species, probably attaining a length of about 15 

 cm. Length of head with opercular apparatus less than the maximum depth of 

 the trunk and exceeding half its length from the pectoral arch to the base of the 

 caudal fin. Length of longest dorsal fin-spines equalling about half the maximum 

 depth of the trunk, and longest anal fin-spine somewhat shorter. About 13 

 scales in a transverse series on the abdominal region, those of the ventral half 

 the more strongly ornamented. 



Bescripfion of Specimens. — This is a rare species known by the type in the 

 Brighton Museum, h\ a small series of specimens in the British Museum, and 

 by three others in the collection of Dr. H. P. Blackmore, Salisbury. 



The general proportions of the fish may be inferred from the type and from two 

 imperfect specimens in the British Museum, nos. 43264 and P. 1952 «. There is 

 also an imperfect small fish from the zone of Holaster suhglohosns at Burham 

 (B. M. no. 41673), which may perhaps be an immature individual of the same 

 species. No. 43264 is shown of the natural size in PI. VIII, fig. 7, and is some- 

 what elongated liy the distortion of the head and tail. The head with opercular- 

 apparatus is about as long as deep. Its length equals less than the maximum 

 depth of the trunk, l)ut more than half the length from the pectoral arch to the 



4 



