1866.] EGEETON ACANTHODES WAEDI. 469 



the length of the tail beyond that point at IJ inch, we arrive at a 

 total length of 7 inches for the perfect fish. The depth of the body- 

 is greatest between the pectoral and ventral fins, where it measures 

 1 J^ inch. The anterior contour of the head is obtusely oval ; and 

 the trunk tapers gradually from the thoracic region to the spring of 

 the tail. On comparing these dimensions with those of the known 

 species of the genus, it appears that this fish was far less bulky, and 

 more elongated, than Acanihodes Bronni from the coal of the neigh- 

 bourhood of Saarbriick, but not so slender as Acanthodes gracilis, 

 from the Permian beds of Klein Neudorf. 



In one or other of the specimens the curious plates encircling 

 the orbit, the pair of slender ossicles representing the lower jaw, 

 and the branchial apparatus are well preserved. The orbital plates 

 are four in number on either side, and are prettily ornamented with 

 minute tubercles or granules. They are very similar in character 

 to the analogous parts in Acanthodes gracilis. The styliform bones 

 forming the rami of the lower jaw are slender and rounded, and 

 about I of an inch in length. The branchial apparatus is com- 

 posed of six arches (as seen in one specimen), whereas Eomer has 

 only represented four in his restoration of Acanthodes gracilis. They 

 are arranged more longitudinally, ^. e. more parallel to the outlines 

 of the back and belly, than in that species. They seem to have been 

 unprotected by any opercular flap. The pectoral spines are long, 

 broad, and scimitar-shaped, the distal end being flattened out and 

 rather blunt ; a deep groove runs parallel to the anterior margin, 

 and a few obsolete depressions traverse the spine obliquely from the 

 inner pectoral margin towards the outer distal extremity : these are 

 not so prominent as the grooves on the pectoral spines of Acanthodes 

 gracilis. The spines are articulated to two strong T-shaped cora- 

 coids, a structural peculiarity common to all the Acanthodidae, and 

 affording, according to Professor Huxley, one of the strongest argu- 

 ments against the placoid aflinities of the family. The spines sup- 

 port fins of large size, the full extent of which is not shown in any 

 of the specimens. The ventral spines are situated, as before stated, 

 at one-third of the antero-posterior length of the fish. They are 

 short, sharp, and recurved. A distinct furrow runs along the front 

 of each. They bear small triangular fins. The anal spine is (next 

 to the pectoral spines) the most powerful of these defensive weapons. 

 It is long, thick, and nearly straight, and is traversed by a deep 

 groove. It is furnished with a large fin extending to within one- 

 third of its point. The dorsal spine is inserted over and behind the 

 anal spine. It is rather weaker than that spine, and is slightly 

 recurved, but resembles it in all other respects. The tail is strikingly 

 heterocercal. The upper lobe tapers off to a fine point ; the inferior 

 lobe commences below with strong fin-rays, which diminish in 

 length and strength as they ascend along the upper margin of the 

 lower lobe. They appear to be composed entirely of ganoin ; in fact 

 each segment has the character and appearance of a thick scale. 

 There is nothing remarkable in the dermal investment ; the scales 

 are smooth externally, and have their under surfaces produced into 



