MR. J. W. KIRKBY ON PERMIAN FISK AND PLANTS. / 7 



spreading out gently from a base half as wide as the maximum 

 breadth of the body to fully two-thirds of that breadth ; it is 

 formed of 17 or 18 rays, as strong as those of the dorsal and anal, 

 and the rays of the ventral lobe are, of course, the longest. The 

 structure of the rays resembles that of the last-mentioned fins : 

 the first segment is of considerable length, being fully four times 

 as long as those that follow it ; the succeeding segments are 

 slightly shorter than the equivalent segments in the anal and 

 dorsal, so as to be wider than long. They appear to bifurcate 

 rarely ; and they are covered with longitudinal scales, like those 

 of the fins just mentioned. Each lobe is protected along its dor- 

 sal and ventral borders with comparatively large fulcral scales. 

 The rays of the caudal, at least those of the central and ventral 

 portions of it, are affixed to long interspinous bones, two rays 

 being attached to each. The rays of the anal and dorsal fins are 

 also attached to interspinous bones, there being in these instances, 

 however, an ossicle to support each ray. 



In well-preserved examples, the head is seen to be bluntly 

 cone-shaped. The gape is comparatively small, and the orbit is 

 large and oval. The opercular bones, which form the great bulk 

 of the head, have a semicircular edge behind, and a surface with 

 rugulose ornamentation. Below and behind the inferior maxil- 

 lary are generally seen the branchiostegal rays, of which there 

 appear to be nine. 



The scales are large, comparatively thick, rhomboidal (vari- 

 ously modified), smooth to the eye, but finely shagreened when 

 magnified, and with plain margins. The dorso-ventral series are 

 arranged in sloping curves ; there are 36 such series along each 

 flank, and 14 or 15 scales in each series in the thoracic region. 

 The lateral line is marked by a longitudinal series of notched 

 scales, somewhat above the centre of the body ; these scales are 

 wider than any of the others on the flank ; the scales above and 

 below the lateral line decrease in size gradually, as they do also 

 from the anterior portion of the body backward. Though the 

 scales have been described as smooth to the eye, it should be 

 mentioned that they are all marked, just within their exposed 

 margins, with two or more lines of increment of great regularity. 



