602 PKOCEEDINGS OF THE GEOLOGICAL SOCIETY. [June 20, 



and marked with concentric growth -lines ; a subcentral boss projects 

 from a shallow depression. The structure of these scales closely 

 resembles that of HoloptycTiius. 



No teeth are found with them, but many ossified vertebrae with 

 neural and haemal spines, and the ventral fin-bones and rajs. 



The best-preserved vertebrae are those along with which the 

 pelvic bones occur. They are longer than broad, slightly constricted 

 in the middle ; their shallow terminal concavities occupy the whole 

 articular surface, and are perforated by a small notochordal foramen, 

 whose area is one-seventh of the whole surface. They decrease in 

 size from before backwards ; the anterior having the following ratio 



, ,1 , . Length 7 5 .. , ,, . 



to the posterior. - — ^— — , -- • — ~ (m tenths). 

 ^ Breadth 11 ' 9 "^ / 



The neural spines, about 2| inches in length, are mostly seen in 

 profile ; their section is pentagonal, much compressed laterally. At 

 a short distance from the base, a slight constriction marks off the 

 articular end, whose convex surface slopes upwards and backwards, 

 so as to form an angle with the axis of the shaft. The arch in- 

 cluded between the two laminae is low and wide. 



The haemal spines, of nearly equal length with the neural, consist 

 of a slender tapering shaft, sigmoidally curved, and terminated at 

 the proximal end by two thin plates triangular in profile and 

 enclosing between them an arch whose height equals one-fourth of 

 that of the whole process. 



Neither haemal nor neural spines are found in actual contact with 

 the vertebrae, whose outer surface is removed, so that the nature of 

 the connexion is not seen. But from being constantly found near 

 the vertebrae, and from the analogy of other allied genera, it may be 

 inferred that they were simply articulated with the vertebrae. 



The pelvic arch consists, on either side, of a bone 3^ inches 

 long, of two triangles united at their apices ; the superior, 2 inches 

 long, is ^ inch broad at its upper end ; the inferior, l-J- inch long, 

 measures 1-| inch along its free or lower margin, to which was arti- 

 culated a row of (probably five) tarsal bones, three of which remain 

 in position. They decrease in size towards one side, the longest of 

 the three being 1-i- inch, the shortest -| of an inch in length ; they 

 are compressed at both ends, constricted and cylindrical in the 

 middle. To the distal smaller ends of these were articulated other 

 similar metatarsal bones, whose number cannot be guessed at ; the 

 only two members of this, row seen in place measure |- of an inch 

 in length. To these were attached the fin-rays, long cylindrical 

 rods of a compact dark enamelloid substance, like that which in- 

 vested the vertebrae and pelvic bones, and traversed by a narrow 

 canal. Their proximal ends are compressed ; distaUy they taper ; 

 but no transverse divisions are present in any of them. 



Locality : Palace, Craig. Airdrie. 



Steepsodus, Huxley. Fig. 3. 



The tooth so named has already been figured in the Journal of the 



