1890.] FROM THE WEALDEN AND PURBECK BEDS. 351 



the support of the haemal arches. There are also long slender ribs 

 and neural spines. 



Apjiendicular Skeleton. — The basal portion of the pectoral fin (p.) 

 consists of stout unarticulated rays, not less than fitteen in number ; 

 but the distal part of the appendage is unfortunately wanting. 



Scales. — There is distinct evidence of a well-developed squamation. 

 The scales are thin, ganoid, and smooth externally, and appear as if 

 deeply overlapping. 



Generic and Specific Determination. — The principal characters of 

 the fossil thus described show that it pertains either to Caturus or 

 Strobilodus ; and, as remarked by von Zittel, the known differences 

 between these two types are so slight that it is probable the latter 

 must only be regarded as a subgenus of the former. Since, however, 

 the obliquity of the mandib'alar suspeusorium is greater and the ossifi- 

 cation of the vertebrae apparently more advanced than in the typical 

 species of Caturus, while the teeth exhibit bases as tumid and as 

 much indented externally as those of the typical Strobilodus, it seems 

 advisable to adopt the latter name for the Purbeckian fossil, whatever 

 its value may eventually prove to be. 



Of this genus, S. gigas, from the Lithographic Stone of Bavaria \ 

 and S. suchoides, from the Kimmeridge Clay of Norfolk", are the 

 only two recognized species ; and the new fossil is distinguished from 

 both by attaining scarcely half the size, by the relative narrowness 

 of the maxilla and mandible, the slenderness of the apical portion 

 of the principal teeth, and the extreme elongation of the hindermost 

 maxillary teeth. It may thus be regarded as indicating a hitherto 

 unrecognized species, to be named S. purbeckensis, from its occurrence 

 in the Purbeck beds, which constitute the highest horizon as yet 

 known to yield remains of the genus in question. 



Genus Mesodon. 

 [A. Wagner, Abh.k.-bay. Akad. Wiss., CI. ii. Bd. vi. 1851, p. 56.] 



Mesodon daviesi, sp. nov. (Plate XXVIII. fig. 5.) 

 A typical member of the Pycnodont genus Mesodon, from the 

 Purbeck beds of Swanage, is indicated not only by the well-preserved 

 fish shown in Plate XXVIII. fig. 5, but also by the head and anterior 

 abdominal region of another individual, which may possibly pertain 

 to a distinct species. The total length of the complete specimen is 

 0*225, the figure being thus one half of the natural size. The fish 

 is round and short, the maximum depth of the trunk immediately in 

 advance of the dorsal fin being somewhat less than the length of the 

 head and trunk to the base of the caudal fin ; while the head and 

 opercular apparatus are contained nearly five times in the total length 

 (including the caudal fin). 



Head and Opercular Apparatus. — The bones of the head are 

 much crushed and obscurely defined, the majority being partly broken 

 away, and some only displaying the fibrous inner aspect. The skull 



^ A. Wagner, torn. cit. p. 75, pi. ii. 



- Thlattodm suchoides, R. Owen, Geol. Mag. vol. iii. (1866), p. 55, pi. iii. 



