MICRODON. 59 



ruga? or pittings, covering only the anterior half of the trunk, and complete only 

 in the lower part of the flank ; traces of fiblets of scales sometimes on the middle 

 of the flank of the caudal region. 



Type Species. — Microdon elegans (L. Agassiz, Poiss. Foss., vol. ii, pt. i, 1833, 

 p. 16, and pt. ii, 1839-44, p. 205, pi. lxix b) from the Lower Kimmeridgian (Litho- 

 graphic Stone) of Solenhofen, Bavaria. 



1. Microdon radiatus, Agassiz. Plate XIV ; Plate XV, figs. 1—5 ; Text-figure 23. 



1839-44. Microdon radiatus, L. Agassiz, Poiss. Foss., vol. ii, pt. ii, p. 208, pi. lxix c, figs. 1, 2. 



1840. Microdon radiatus. K. Owen, Odontography, p. 7'S, pi. xliii, fig. 1 [microscopical structure of 



teeth]. 

 1895. Microdon radiatus, A. S. Woodward, Catal. Foss. Fislies Brit. Mus., pt. iii, p. 223. 



Type. — Imperfect fish. 



Specific Characters. — A species attaining a length of about 12 cm. Maximum 

 depth of trunk somewhat less than total length to base of caudal fin ; head with 

 opercular apparatus occupying scarcely a quarter of total length of fish. Splenial 

 teeth of principal series with well-rounded ends, wider than the two outer series, 

 of which the outermost is considerably the larger. Vertebral axis at origin of 

 dorsal fin slightly above middle line of trunk. Dorsal fin with about 40, anal fin 

 with 30 supports. Each ridge-scale with three or four very prominent denticles, 

 inclined and increasing in size backwards, flank-scales delicate, marked with more 

 or less radiating rugae between the pittings. 



Description, of Specimens. — The type specimen, originally in the collection of 

 H. E. Strickland, exhibits the general proportions of the fish, with the characteristic 

 stout ventral ridge-scales, but somewhat distorted in the region of the pectoral 

 arch and lacking the greater part of the fins except the caudal. A smaller speci- 

 men in the Dorset County Museum (PI. XIV, fig. 1) shows still better the shape of 

 the fish as noted in the specific diagnosis above ; while a larger specimen in the 

 British Museum (PI. XIV, fig. 2) displays the principal characters of the trunk. 



In the skull (PI. XV, fig. 1) the facial region as usual is somewhat bent down- 

 wards, while the tooth-bearing surface of the vomer is in a plane nearly parallel to 

 that of the base of the cranium. The cranial cartilage is well ossified, one speci- 

 men in the British Museum (no. P. 1627 a) showing apparently the exoccipital, 

 basioccipital, and pro-otic elements, while others seem to exhibit a postfrontal 

 (sphenotic) and perhaps an alisphenoid or orbitosphenoid (PI. XV, fig. 1, ors.). 

 The cranial roof is completely covered with membrane bones, which are marked 

 with a more or less radiating reticular ornament. A small narrow median element 

 which forms the crest behind the frontals, may be described as the supraoccipital 

 plate (PI. XV, fig. 1, socc), and bears a few close rows of small recurved denticles 

 along its edge. It is more or less incompletely fused behind with the first ridge- 



