from the Scotch Old Red Sandstone. 299 



attached to the tuberosity of the dorsal plate. The dorsal plate 

 is 2^ inches long and l^ wide, with straight parallel sides, not 

 being perceptibly narrower in front than at the lateral angles, in 

 which it differs from the C. pusillus (M^Coy) as well as in size. 



Rare in the black flags of Orkney. 



{Col. University of Cambridge.) 



Coccosteus? trigonaspis (IVPCoy). 

 Sp. Char. Mesial ventral plate sub trigonal, slightly convex, 13 

 lines long and 7 lines wide at the lateral angles, which are 

 only 2 lines behind the rounded or very obtusely angular an- 

 terior end ; lateral posterior margins straight, converging to 

 form the retral point ; four or five irregular rows of tubercles, 

 half a line in diameter, and less than their diameter apart, run 

 round the margin, leaving a central, ovate, convex space more 

 obscurely tubcrculated ; each tubercle consists of a hemisphe- 

 rical smooth centre (frequently perforated in the middle), sur- 

 rounded by a thickened base which is radiatingly ridged, in- 

 tervening space irregularly dotted. 



This beautiful species is easily distinguished from all others 

 by the shortness of the anterior end of its ventral mesial plate, 

 which is the only part yet known. The tubercles resemble those 

 of a small Cidaris or Asterolepis, 



(Col. University of Cambridge.) 



(Acanthodidce.) 



Chiracanthus pulverulentus (M^Coy) . 

 Sp. Char. Elongate, fusiform, tapering very gradually from the 

 pectorals, where the depth is little more than one-sixth of the 

 length ; tail moderate. Innately forked ; the bony ray of the 

 dorsal fin is slightly nearer the anal than the ventral fins, 

 those latter being half-way between the pectorals and anal ; 

 the ventral spines are about half the depth of the body at their 

 base, the others are about two-thirds of the depth ; scales flat, 

 rhomboidal, but the length and width nearly equal, appa- 

 rently not imbricated, the posterior, inferior angle tumid, 

 pointed ; seven scales occupy a space of two lines ; surface 

 dull, covered with an exceedingly minute, crowded granula- 

 tion (only visible under a strong lens). Length 8 inches. 



The squamation of this species is so peculiar that a compa- 

 rison with its congeners is rendered unnecessary; in general 

 appearance it resembles the C. Murchisoni (Ag.). The head is 

 imperfect, but seems rather pointed and about one-sixth of the 

 entire length. 



Rare in the old red flags of Orkney. 



(Col. University of Cambridge.) 



21* 



