from the Scotch Old Red Sandstone. 311 



Holoptychius Sedgwickii (M'Coy). 



Sp. Char. Body fusiform, very thick, depth in the middle one- 

 third of the length, abruptly narrowed towards the tail, the 

 pedicle of which at the base of the anal and dorsal fins is 

 scarcely half the depth of the body ; head more than one-fourth 

 of the length ; tail very short, nearly square, the thick, articu- 

 lated, frequently branched rays developed from the under 

 side, forming a broad triangular caudal fin, obliquely trun- 

 cated on its posterior margin ; dorsal rather larger than the 

 opposite anal fin, both semi-elliptical, twice as high as long; 

 the anal about one-third the length of the base in advance of 

 the caudal ; ventral fins broad, their length about equalling 

 their height, rather more than the length of their bases in 

 advance of the anal fin ; lateral line nearly medial, strongly 

 marked : scales thin, rounded, those of the flanks half an inch 

 in diameter, subtrigonal, posterior margin semicircular, con- 

 cealed anterior margin very broad, subtruncate, with very 

 minute radiating punctate strise ; immediately in front of this 

 a small space towards the middle of the scale is covered with 

 a distinct granulation (frequently but not always seen when 

 the scales are in situ) ; all posterior to this, or the constantly 

 exposed portion covered with a minute, longitudinal, irregu- 

 larly flexuous, striate punctation, intermixed with numerous 

 sharp, narrow, irregularly interrupted, longitudinal thread-like 

 ridges, of very irregular number and length, but usually two or 

 three times their diameter apart; the exposed part of the scales 

 of the flanks, when in situ, is about one-third higher than 

 long. Teeth conical, one-third longer than wide, half the dia- 

 meter of their bases apart. 

 Length 11 inches, depth nearly 4 inches; length of teeth f of 



a line. 



This species, like the H. Flemingii (Ag.), is remarkable for 

 being found on its side, indicating apparently a compressed, 

 instead of a depressed form ; it also resembles that species in the 

 sculpturing of the scales, but has them (in the same parts of the 

 body) smaller, more rounded, and the exposed portion much less 

 high in proportion to their length. 



Not uncommon in the old red sandstone flags of Orkney. 



(Col. University of Cambridge.) 



Conchodus (M^Coy), n. g. 



Gen. Char. (Teeth in pairs in each jaw as in Ceratodus ?) ; each 

 tooth large, somewhat semicircular, pointed in front, sub- 

 truncate behind, deeply concave on the grinding surface; 

 internal margin straight, thickened, and with an abruptly 



