FISH OF THE OLD RED SANDSTONE. 33 



about equal to the depth of the body at the ventrals in the 

 former, but exceeding it in the present species. What renders 

 the C. lateralis most remarkably distinct from the other species 

 of this and the allied genera, is the presence of a very strongly 

 marked lateral line. 



Rather rare in the old red sandstone flags of Orkney. 



[Col. University of Cambridge.) 



Diplacanthus gibbus (M'Coy). 



Sp. Char. Very thick, fusiform, depth of the body behind the 

 pectorals equal to the distance between the two dorsal spines ; 

 the dorsal spines are equal, about 1 inch long and 1 line wide, 

 the first dorsal less than the depth of the body at its base ; 

 anal spine much shorter than the second dorsal ; scales rhom- 

 boidal, length and width nearly equal, each with a large, ver- 

 tically diagonal, oval gibbosity occupying nearly its entire area, 

 about five scales in one line, surface seems very minutely gra- 

 nular. Length about 4i inches, greatest depth 1^ inch. 



This species has more equal-sided scales than the D. striatus 

 (Ag.), and is nearly double the proportional depth ; the spines 

 are longer and more slender than in the D. crassispinus (Ag.), 

 besides the difference in the scales. 



Very rare in the old red flags of Orkney. 



[Col. University of Cambridge.) 



Diplacanthus perarmatus (M^Coy) . 



Sp. Char. Body thick, short, fusiform ; tail very short, nearly 

 square, its width only two-thirds the length of the second 

 dorsal spine, the upper lobe projecting but little beyond the 

 lower ; spines smooth, extremely long, first dorsal equal in 

 length to the space between the first and second dorsals, 

 slightly less than the depth of the body at its base, gently 

 curved ; posterior spine straighter and about one-eighth longer 

 than the anterior ; pectoral spines half the length of the second 

 dorsal ; anal spine curved, only two-thirds the length of the 

 second dorsal ; ventral, medial and thoracic spines slightly 

 curved and of moderate length ; scales slightly higher than 

 wide, nearly flat, minutely granulated (the impressions only 

 seen), about three in the space of one line. Length from the 

 base of the pectoral to the tip of the tail 4| inches. 



This is most allied to the D. longispinus (Ag.), but has still 

 longer spines, the second dorsal being especially remarkable ; the 

 dorsal spines are much longer in proportion to the distance be- 

 tween them and the depth of the body, the anal spine being on 

 the other hand comparatively shorter ; the tail is still smaller and 

 more equal-lobed, and the scales much smaller and with the pro- 



c 



