1890.] FROM THE "WEALDEN AND PURBECK BEDS. 349 



rakers (the fragmentary rods of the type specimen), each of these 

 being smooth and elongated, with a slight constriction immediately 

 above its base, and tapering to a point distally. 



Vertebral Column. — A single centrum attached to the occipital 

 portion of the type specimen (Plate XXVIII. fig. 1 a) shows that 

 the vertebrae were completely ossified, while the second Wealden fossil 

 and some of the Purbeckian specimens reveal the principal characters 

 of the anterior part of the vertebral column. The centra are narrow 

 and distinctly amphicoelous, much deeper than broad, and marked 

 on the sides by fine transverse striations extending between a thick- 

 ened rim anteriorly and posteriorly ; a pair of deep pits on the upper 

 aspect accommodates the neural arch, and there is a similar pair of 

 pits on the ventral aspect for the insertion of a haemal arch. The 

 only traces of attached peripheral elements on the sides of the centra 

 consist in a small, faint, rounded pit or rugosity on four or five of the 

 anterior vertebrae in the so-called Lepidotus, which may have sup- 

 ported an intermuscular bone. The first vertebral centrum, articulat- 

 ing with the basioccipital, is composed of two thin discs fused together 

 (Plate XXVIII. fig. 3), but the others are all simple, each bearing its 

 own arch. The neural spines (Plate XXVIII. fig. 4) are long and 

 slender, fixed to delicate, low arches, with prominent zygapophyses ; 

 and if the fossil that best displays these structures gives equally 

 reliable indications of the haemal elements, the latter have the form 

 of very feebly developed ribs. Two long curved bones in the second 

 of the large AVealden specimens are also at first sight suggestive of 

 ribs, and seem to indicate a greater development of these structures 

 than is here shown; but the elements in question are not certainly 

 determinable and may be branchiostegal rays. 



Generic and Specific Determination. — That the fossils now de- 

 scribed pertain to the genus Oligopleurus seems evident from the 

 form and proportions of the jaws and dentition, the characters of 

 the vertebral centra, and the slight development of the neural and 

 haemal arches. The absence of scales is explained by their extreme 

 tenuity in the fish of the Lithographic Stone, and the coarse nature 

 of the matrix in which the new Wealden and Purbeck specimens 

 occur. 



These fossils, however, scarcely suffice for a specific determination, 

 and unless the small immature individual from the Purbeck beds, 

 shown, of shghtly reduced size, in Plate XXIX. fig. 3, be the young 

 of the form under consideration, no precise diagnosis can as yet be 

 attempted. That the larger fossils now described represent a 

 distinct species from the typical O. esocinus, seems to be indicated 

 by the narrowness and greater relative depth of the anterior vertebrae 

 in the English specimens ; and they may thus be provisionally 

 named O. vectensis, from the discovery of the first and best-preserved 

 fossil in the Isle of Wight. If, however, the small fish just referred 

 to prove to be truly referable to the same species, it will readily be 

 distinguished by its much more slender proportions — the depth of 

 the trunk at the position of the pectoral arch being comprised nearly 

 seven times in the total length, whereas in O. esocinus the same 



