294 MB. J. W. DAVIS ON HETEEOLEPIDOTUS GEAJS"DIS, 



the latter was a fish considerably deeper in proportion to its 

 length than the present one ; and whilst the form of this spe- 

 cimen was slim and graceful, its fins are longer, more powerfully 

 developed for rapid motion than those of S. sauroides, Egert. (op. 

 cit. pi. 2). The scales on the dorsal and median surfaces, repre- 

 sented natural size on my Plate VII. fig. 2, are rhomboidal in 

 outline: those on the ventral surface are larger and elongated, 

 gradually becoming still longer as they near the ventral line, 

 where the scales are twice as long as broad. The scales are thin 

 and apparently flesible, which may account for their not being 

 very extensively preserved. They are covered with small pustu- 

 lations on a thin coating of ganoine. Thus, whilst the scales are 

 similar in form and possess the distinguishing characteristics 

 of the Heterolepidoti, as defined by Sir P. Egerton, they difi'er 

 in being very thin and pustulate. The exposed bones of the 

 cranium are also covered with rugose pustulations on the sur- 

 face of the ganoine. In some instances the pustules attain 

 •1 inch in diameter. The remaining bones of the head are more 

 or less smooth or striated. The lower jaws are 5 inches in 

 length, and a number of teeth are scattered about, some of them 

 in small patches, indicating that they were closely aggregated on 

 the surface of the jaws. The teeth are small, about 1 inch in 

 length, conical and pointed. If the fish had a series of larger 

 teeth, they have entirely disappeared. The external cranial 

 plates are preserved, and the scapulo-coracoid arch supporting 

 the large pectoral fins is strong and powerfully built. 



The anterior portion of the vertebral column is unfortunately 

 enveloped in iron pyrites ; the posterior part, behind the anal fin 

 to the base of the caudal, consists of about 20 vertebrae ; the 

 termination of the column, composed of an additional 9 vertebrae, 

 is deflected so as to enter the upper lobe of the tail, the latter 

 having a decidedly heterocercal form. The lower lobe consists 

 of 16 rays, which are attached to the under surface of the ver- 

 tebrae by a number of broad, somewhat spatulate and flattened, 

 hsemal spines, expanding so as to form a rounded termination for 

 articulation with a second series of intermediate bones, to which 

 the fin-rays are attached. The latter consist of a series of 

 jointed ossicles ; the longest rays are 6*5 inches in length, and 

 repeatedly dichotomize. The lower margin of the tail is fur- 

 nished with a long series oi imbricating fulcral rays. Sur- 

 rounding, and attached to the caudal vertebrae, of which nine 



