28 FOSSIL FISHES OF THE ENGLISH CHALK. 



2. Homonotus rotundus, sp. nov. Plate VII, fig. 8. 



2'//2?e. — Distorted fish ; British Museum. 



Specific Characters. — A smaller species than the type of the genus with more 

 deepened trunk. Length of longest dorsal fin-spines not exceeding one-third the 

 maximum depth of the trunk ; fourth anal fin-spine at least as long as the longest 

 dorsal fin-spine. 



Description of Specimens. — This small fish is known by two small specimens in 

 the British Museum, the largest (no. P. 5682) representing an individual perhaps 

 10 cm. in total length, with a maximum depth of about 4 cm. The dorsal region 

 of another fish as large as the latter is also preserved in Mr. Dibley's collection. 



The type specimen, which is much distorted, is shown of the natural size in 

 PI. VII, fig. 8. Its head is almost destroyed, the remains only comprising recognis- 

 able portions of the pectinated antorbital. The trunk must have been originally 

 almost orbicular with a much contracted caudal pedicle. The vertebral column is 

 distorted, but so far as it can be compared, it resembles that of H. dorsal is. The 

 dorsal fin (d.) clearly extends along the greater part of the back, and its anterior 

 portion consists of 12 slender spines, each marked with a longitudinal groove and 

 fixed to a winged support. The foremost four of these spines rapidly increase in 

 length, the next four are about equal, and the last four are slightly the longest. 

 The length even of the latter must have been contained at least three times in the 

 maximum depth of the trunk. Behind the spines there seem to be traces of not 

 less than 15 articulated dorsal fin-rays, arranged in a series extending quite to the 

 base of the contracted caudal pedicle. Among the remains of the anal fin (a.) the 

 fourth anterior spine is well preserved, and it is as long as either of the four hinder- 

 most dorsal fin-spines. It is followed by not less than 13 articulated rays, and the 

 anal fin must have terminated exactly opposite the end of the dorsal fin. The 

 scales are large and thin, as usual, and some of them exhi])it traces of their hinder 

 pectination. 



The larger specimens already mentioned do not display any additional 

 characters of the species. B. ]\I. no. P. 5082 exhibits the triangular supraoccipital 

 crest of the skull. 



TTorizons and Localities. — The type specimen was obtained by the late Mr. 

 Harris of Charing from Page's Pit, Westwell, near Charing, Kent, and evidently 

 belongs to the zone of Holaster .suhrjlohosus. The largei' specimen, from the Harford 

 Collection, is of uncertain origin. Mr. Dibley's specimen was discovered in the 

 zone of Holaster suhglohosus, Blue Bell Hill, Burham. 



