70 FOSSIL FISHES OF THE ENGLISH CHALK. 



Anterior abdominal vertebral centra about three times as long as deep, those beyond 

 less elongated, and those in the hinder half of the abdominal region with large 

 transverse processes. Dermal scutes of moderate size and narrow, more or less 

 ornamented with short ridges and spinous tubercles ; those on the anterior 

 abdominal region not excessively attenuated ; those on the dorsal and ventral 

 borders of the posterior abdominal and caudal regions bearing a slender backwardly 

 directed uncinate spine. 



Description of Specimens.— The type specimen in the Mantel! Collection (nos. 

 4132-33) is an imperfect small fish preserved in the counterpart halves of a block 

 of chalk from the neighbourhood of Lewes (PI. XVI, figs. 1, 1 a). The abdominal 

 region is sharply bent upon itself at about its middle ; the end of the caudal region 

 and all the fins are wanting. The characters of the skull and dentition are feebly 

 indicated; while the vertebral column and dermal scutes are exhibited in a 

 tolerably satisfactory manner. 



The cranium, clearly identical with that of the type specimen, is best shown 

 from above and below in B. M. no. 49793 (PI. XVI, figs. 2, 2a) and in the 

 Willett Collection no. 115 (fig. 3). The postorbital region occupies about one quarter 

 of its total length, and is as long as broad, witli nearly parallel sides, and the 

 occipital border excavated "with a sharp re-entering angle. The frontal region 

 between the orbits is exceedingly constricted, while the rostrum is very slender 

 and truncated in front. All the external bones are ornamented with a few 

 delicate longitudinal ridges, occasionally subdivided into tubercles. When the 

 roofing bones are removed, as shown in fig. 2, the well-ossified but small supra- 

 occipital (wee.) can be observed beneath, bearing a slight vertical median crest 

 behind ; but it was completely covered by the relatively large parietals. These 

 bones (pa.) are shown in external impression in fig. 2 a, from their inner aspect in 

 fig. 3. They are an unsymmetrical pair of quadrangular plates, meeting through- 

 out their length in a slightly wavy suture, and marked on their outer face by 

 about two longitudinal ridges which extend from border to border, while other 

 short ridges and tubercles are observed behind. The squamosals (.svy.) are small 

 long and narrow plates at the postero-lateral angles of the skull, scarcely produced 

 further forward than the parietals. The frontals (//•.) extend and expand back- 

 wards to form at least half of the postorbital region, and these are not a quite 

 symmetrical pair. As shown in fig. 3, their narrow interorbital region rises on 

 each side into a small supraorbital flange. Their anterior ends, as shown in fig. 2, 

 seem to have been a little expanded again on the rostral region. As indicated by 

 the impression, fig. 2a, the outer face of the frontals is ornamented with a few 

 longitudinal ridges, which do not quite reach the hinder margin and are not con- 

 nected or correlated with the ridges on the parietals. The well-ossified, long and 

 narrow mesethmoid (eth.) is very slightly expanded in front, and its anterior 

 extremity is curiously excavated in such a manner as to give it the appearance 



