148 A. Smith Woodimrd — Fish Fauna of Purhech Beds. 



"bifurcating rays, but nothing can be discerned as to their supporting 

 elements. The dorsal fin arises about the middle point of the trunk, 

 though not quite at the summit of the dorsal convexity : it is imperfect 

 in front and at the distal border, but comprises about thirty-five well- 

 spaced delicate rays. The anal fin is similar, but much shorter, 

 comprising not more than twenty-six rays. The caudal fin is stouter 

 than the other median fins, and its rays, to the number of about 

 eighteen, are produced into more prominent bifurcations distally. 



Squamatioti. — Remains of thick scales, of the usual form, occur over 

 the anterior half of the fish, with prominent ridge-scales (about 

 fourteen in number dorsally), and extending as far as a line joining 

 the origin of the dorsal and anal fins. Xo superficial tubercular 

 ornament can be observed, but this circumstance may well be due 

 to imperfection in preservation. On the caudal region there is no 

 evidence of any squamation ; but a series of small, elongated, tubular 

 ossifications seems to show that even in its hinder half the course of 

 the lateral line was protected by hard parts. 



Sjjecifio Determination. — The fish thus described is much smaller 

 than any example of Mesodon hitherto known, and is probably another 

 adult member of the remarkably dwarfed fish-fauna characteristic of 

 the Lower and Middle Purbeck in the Vale of Wardour. It is 

 distinguished from 31. Baviesi, the only described Purbeckian species, 

 by its larger head, deeper trunk, and the slightly smaller number of 

 rays in its dorsal and anal fins. With M. macropterus, however, from 

 the Lithographic Stone of Bavaria, it is almost identical, except in 

 size, agreeing with this fish in its general proportions and the number 

 of rays in the dorsal fin. The anal fin has four or five rays fewer than 

 usual in M. macropterus, and the scales seem to cover quite half of 

 the trunk. Until the discovery of more specimens with the dentition, 

 Mr. Andrews' fish may therefore be provisionally placed in the last- 

 mentioned species as a distinct dwarf variety named parvus. 



Sori%on and Locality . — Middle Purbeck: Lime Kiln Quarry, Teffont. 



Mesodon^ sp. 



Another specimen of Mesodon obtained by Mr. Andrews from the 

 Middle Purbeck of the Lime Kiln Quarry, Teifont, is too imperfect 

 for specific determination, but is worthy of a brief notice. The total 

 length of the fish is about 0'13 m., and the proportions of its head and 

 trunk are as in M. macropterus. All the teeth exhibited, including 

 those of the principal splenial series, are indented at the apex, and 

 some of the round lateral teeth are also crenulated. The squamation 

 is preserved over half the trunk, and at least seventeen vertebral 

 arches are indicated in the caudal region. The median fins are very 

 imperfect, but the caudal fin clearly exhibits the form characteristic 

 of Mesodon. 



Macrosemius Andrewsi, sp. nov. Plate YII. Fig. 3. 



This species is founded upon a small specimen, 0'32 m. in length, 

 without the caudal fin. Both sides of the fossil are preserved, and 

 one is shown of the natural size in PL VII. Pig. 3. The length of the 

 head with opercular apparatus considerably exceeds its maximum 

 depth, and is contained about three-and-a-half times in the total 



