1866.] rouNG — rLATYsoMus. 303 



and parvulus. PI. parvus has been merged by King (Permian 

 Possils) in PI. striatus ; PI. intermedins , Miinst., by Geinitz in PI. 

 gihhosus ; and PI. Fuldai, Miinst., by the same author, in PI. macrurus. 



Platysomtjs pakvulfs, Ag. 



Body with a gentle ventral convexity ; the dorsal highest point an- 

 gular, anterior to the middle of the back. The nuchal margin nearly 

 in a line with the slope of the face. Head triangular ; its length equal 

 to one-fourth of that of the body. Orbits of moderate size and close 

 to the upper margin of the head. Jaws armed with slender conical 

 teeth, those in the lower slightly larger and more distant than those 

 in the upper jaw. Facial and opercular bones vertically striated ; 

 cranial bones and mandibles finely tuberculated. Pectoral arch 

 moderately strong; fin with narrow base, and expanded rounded 

 extremity. The dorsal commences at or behind the middle of the 

 back, slightly in front of the anal, and terminates opposite the latter 

 at the caudal root ; the anterior rays are, in both, the longest, the 

 others abruptly shorten and maintain nearly the same length back- 

 wards; the former bifurcate only at their extremities, the latter 

 divide repeatedly, forming a fine fringe. Tail heterocercal, equilo- 

 bate. The anterior margins of all the fins are protected by fine 

 fulcral scales ; the nearly square articles of the rays are covered by 

 striated scales. The scales are oblong, higher than broad, they 

 diminish in size towards either margin of the body and towards the 

 tail. They are ornamented by parallel vertical striae, which are 

 rather more than their own breadth apart, and have their crests 

 finely tuberculated. The lepidopleura continue distinct as far as 

 the root of the tail, whose upper lobe is covered by a single series of 

 large pointed ridge- scales. The upper and lower edges of the body, 

 anterior to the opposite fins, are also protected each by a single row 

 of small scales, modified into smooth tubercles, which support small, 

 usually recurved, denticles : of these there are generally four on each 

 ventral, and three on each dorsal tubercle. With these tubercles 

 the lepidopleura are connected above and below. The lateral line 

 is nearest the dorsum, towiirds which it is gently arched in front, 

 terminating at the upper angle of the operculum. 



Plattsomus pakvultts, var. 



The body is more oval than in the typical form above described, 

 its greatest depth is marked by no angular dorsal peak. The caudal 

 pedicle is longer. The striae on the scales are finer, barely their 

 own width apart, and their crests are smooth. 



The species was founded by Agassiz on specimens at Leeds, but 

 was not described by its author. My reference to it of the numerous 

 specimens from the IS'orth Staff'ordshire Coal-field is confirmed by 

 Prof. W. C. Williamson, who, in his valuable memoir "On the 

 structure of Scales and Teeth," communicated to the Eoyal Society 

 in 1849, describes the scales of PI. parvulus as " covered with deep 

 grooves and intervening ridges running nearly parallel with the long 

 axis of the scale which, as in Gyrodus, really represents its breadth: 



