40 PISH OF THE OLD RED SANDSTONE. 



only as far as the central point, where it abruptly terminates 

 to allow of the imbrication of the remainder of the scale on 

 the next behind; bones of the head covered with granules 

 which are sometimes confluent into short ridges ; teeth small, 

 conical, nearly equal. 



In form, number and position of the fins and structure of the 

 tail these fishes resemble Diplopterus, while the imbrication of 

 the scales, as well as their sculptured, instead of simply porous 

 surface, places them close to HolopUjchius, and in a different 

 family of Agassiz^ system from the former ; while from the lat- 

 ter they, differ in form, number and position of the fins, struc- 

 ture of the tail, and in the ridge on the under side of the scales, 

 which reminds us of what we see in Osieolepis and many other 

 fishes with juxtaposed scales, but instead of extending entirely 

 across the scale, it only reaches half-way, the half-ridge of one 

 scale joining that of the next behind and before when in their 

 natural imbricated position. The Gyroptychii are thus interme- 

 diate between Holoptychius and Diplopterus, and serve to con- 

 nect the great groups of Ccelacanth and Sauroid fishes to which 

 those genera respectively belong, having at the same time a style 

 of sculpturing of the scales peculiar to themselves and easily re- 

 cognizable. There are two imperfectly known and imperfectly cha- 

 racterized genera of M. Agassiz, Ghjptopomus and Platygnathus, 

 which require a few words in connexion with the present fishes. 

 The first of those genera is founded on a short, thick, fusiform 

 sauroid fish, with simply juxtaposed, rhomboidal, granulated 

 scales ; the fins being nearly unknown. The slender form, and 

 the shape, sculpturing and imbrication of the scales are sufiicient 

 distinctions, the fins being unknown. Platygnathus is a genus 

 founded by Agassiz on the jaw of one fish and the tail of another ; 

 the jaw agrees nearly with Bothriolepis, but has fewer laniary 

 teeth and needs no comparison with Gyroptychius ; the tail por- 

 tion is more analogous, but the great scales seem to have simply 

 the structure of Holoptychius, and the fins are developed beyond 

 all comparison ; further, this genus is founded on such imperfect 

 and perhaps discordant materials, and the jaw seeming to have 

 been most in view in naming and defining the genus, it is ob- 

 vious that even an identity between one of those elements and 

 the present perfectly known type would not invalidate Gyropty- 

 chius as a genus. Judging from the figure and description of 

 M. Agassiz, however, there seems, as above noted, to be no great 

 affinity between them. 



Gyroptychius angustus (M^Coy). 

 Sp. Char. Head semi-oval, obtusely pointed, about one-sixth the 

 entire length; depth of the body greatest immediately be- 



