58 



BEITISH FOSSILS. 



has rendered to Palaeontology I propose to designate the subject of 

 this article by his name. 



Description. — Although somewhat longer than the Acanthodes 

 pusillus from Tynet Burn, this is, nevertheless, one of the smaller 

 species of the genus. The length of the only specimen found in 

 tolerable preservation is about 2^ inches. The depth of the 

 the body is four-tenths, and caudal pedicle two-tenths of an inch. 

 It differs remarkably from Acanthodes pusillus in these relative 

 dimensions, being a thicker fish and less elegant in its pro- 

 portions. The latter species is usually found doubled up upon 

 itself, as if it had died a violent death. The Caithness species is 

 also recurved, as if it had met with a similar fate ; but, owing 

 to the greater rigidity of the body, the distortion has been less 

 excessive. The head seems to be large in proportion to the body, 

 but this appearance may be due to the mutilated condition of this 

 portion of the specimen. Owing to a forcible disruption of the 

 integuments at the junction of the head and thorax, the former has 

 been thrown up and crushed vertically, in consequence of which its 

 natural proportions are disfigured by the lateral projection of the 

 component bones. The pectoral fins remain in their proper position. 

 They are supported by two strong spines, slightly recurved. The 

 portions of the thoracic arch, to which these spines are attached, are 

 seen sloping uj)wards from the articulation. They probably repre- 

 sent the coracoid bones. They are of slighter proportions than the 

 corresponding bones in the genera Gheiracanthus and Diplacanthus. 

 The ventral fins are situated about midway between the pec- 

 toral and anal fins. They are furnished with two spines, more 

 slender than the other fin spines, but longer in proportion than 

 in any other species of this genus. The dorsal fin is placed in 

 a more forward position than the corresponding organ in the allied 

 species. Instead of being slightly more remote than the anal fin, 

 it is immediately above it. The spine which carries the fin is the 

 strongest of the set. It is more curved than the dorsal spine of the 

 other species of contemporaneous origin. The anal spine is also 

 strong and curved. All the fin spines are ornam.ented with three 

 or four longitudinal grooves. The tail is very broad for the size of 

 the fish. The upper lobe projects beyond the lower lobe to a con- 

 siderable extent, but does not taper ofi" so gradually as in other 

 species. The appearance of a bifurcation at the extremity is due to 

 a separation of the integuments, either from pressure or decomposi- 

 tion. The scales are very minute, at the same time they appear to 

 have been coarser than the scales of AcanthodeB pusillus. 



