38 FISH OF THE OLD RED SANDSTONE. 



head very obtusely rounded, nearly semicircular, depressed, 

 twice as wide as long, the length being only two-thirds the 

 depth of the body ; scales thick, nearly equilateral except on 

 the flanks, where they are one-third higher than long, length 

 of each about one line, surface minutely and uniformly punc* 

 tured under the lens, the pores rather distant ; two anal fins 

 very small, ovate, their own length apart, the second touching 

 the caudal ; one large triangular dorsal fin, longer than high, 

 opposite the space between the two anal fins (anterior dorsal 

 not seen). 



Easily distinguished from the other Osteolepi by its very wide, 

 short figure, and from the great width of the head it is almost 

 always found with the anterior part of the body crushed verti- 

 cally. The teeth are very small, close and slender. 



I have seen five specimens from the old red schists of Caith- 

 ness and Orkney. 



{Col. University of Cambridge.) 



Tripterus (M'Coy), n. g. 

 Gen. Char. General shape of the body and form of the plates of 

 the head and body as in Osteokpis, but having only one dor- 

 sal fin, which is precisely over the first anal fin. 

 The fishes of this genus are very much allied to Osteolepis in 

 general habit, but instead of having two dorsal alternating with 

 two anal fins, there is but one dorsal, which instead of alterna- 

 ting with or being vertically over the interval between the anal 

 fins (as would be the case in Osteolepis, if only one fin was pre- 

 served), is precisely over the first anal as in Diplopterus, which it 

 also greatly resembles, but from which it differs in wanting the 

 second dorsal, and in having a perfectly heterocercal tail — a cha- 

 racter which I have ascertained does not exist in Diplopterus, 



Tripterus Pollexfeni (M'Coy). 

 Sp. Char. Ovate, gradually tapering from the head, which is 

 broad, depressed, semi-elliptical, obtusely pointed in front, its 

 width at base equal to its length, and being about one-fifth 

 the entire length of the fish ; pectoral fins small, broad, ovate, 

 their height about two-thirds the width of the body at their 

 base ; tail small, perfectly heterocercal, retral margin very 

 concave, and the upper lobe twice the length of the lower ; two 

 anal fins nearly equal, triangular, one-third higher than long, 

 rather more than their own height apart, the second almost 

 touching the caudal fin ; dorsal fin narrow, ovate, almost twice 

 as high as long, precisely over the first anal ; scales rhom- 

 boidal, those of the body flat, about one-third higher than 

 long, those of the tail longitudinally gibbous, lozenge- shaped, 

 and about twice as long as high ; under the lens they are all 



