22 WEALDKN AND PURBECK FOSSIL FISHES. 



Type Species. — Undina penic'dlata (Miinster, loc. cif. and A. Wagner, Abhandl. 

 math.-phys. CI. k.-bay. Akad. Wiss., vol. ix, 1863, p. 096) from the Lithographic 

 Stone (Lower Kimraeridgian) of Bavaria. 



1. Undina purbeckensis, sp. nov. Plate IV, fig. L 



Ti/pe. — Imperfect fish ; British Museum. 



Specific Characievs. — A stout species attaining a length of at least 40 cm. 

 Length of head with opercular apparatus about one quarter the total length of 

 the fish, and somewhat less than the maximum depth of the trunk. Rays of first 

 dorsal and caudal fins not expanded in the distal part, where the articulations are 

 not very close ; first dorsal fin with ten rays, caudal fin with about twenty rays 

 above and below. Scales ornamented with coarse elongated tubercles, which are 

 irregularly and rather sparsely arranged, shortest and most numerous on the 

 dorsal scales, longest and fewest on the ventral scales. 



Description of Specimen. — This species is known only by the single imperfect 

 fish, shown of one half the natural size in PI. IV, fig. 1. Of the head very little 

 remains, but its shape and proportions are indicated by a fragment of the cranium 

 at the bend of the frontal profile and by the nearly complete lower edge of the 

 mandible (or perhaps gular plate) in cross-section. The hinder limit is marked Ijy 

 an imperfect impression of the clavicle. Part of the smooth outer face of the left 

 pterygoquadrate bone is seen in position, and a displaced imperfect ceratohyal 

 occurs beneath it. The neural arches of the vertebral axis of the trunk are well 

 preserved, and about forty-five can be counted as far as the origin of the caudal 

 fin, the hinder arches of the series gradually becoming longer and stouter. The 

 ribs, seen only in the hinder half of the abdominal region, are small and delicate; 

 but the liEemal arches in the tail are larger and more nearly symmetrical with the 

 opposed neurals. 



Of the paired fins, only one of the characteristic pelvic bones {plv.) remains, 

 showing that the corresponding fin was inserted closer to the pectoral arch than 

 to the tail. The ten stout rays of the first dorsal fin are distinct (rf^), but their 

 laminar support is covered by the scales. No denticles are seen upon them, but 

 there are shallow pits on the articulated distal portion of some rays indicating their 

 original presence. The forked support for the second dorsal fin is preserved {cV), 

 and there are also some traces of the comparatively delicate rays. The anal fin is 

 represented only by displaced fragments {a). The caudal fin, as usual, is preceded 

 by two or three free supports above, probably also below ; and its total number of 

 rays cannot have been less than twenty above and below. The characteristic 

 denticles are seen on some of the rays in the anterior part of the fin. 



Many of the scales are sufficiently well preserved to exhibit their characteristic 

 ornament. Near the dorsal border between the two fins some comparatively 



