436 NATURAL SCIENCE. Jone, 
The Acanthodian fishes, discovered in Palaeozoic rocks from the 
Lower Devonian upwards, have always presented difficulties to 
systematists ; but it is now generally agreed that they are a peculiar 
order of sharks. As to the precise significance of several parts of 
their skeleton, however, there is still much disagreement, and Dr. 
Fritsch himself wisely refrains from very definite expressions of 
opinion. 
The general aspect of the type-genus Acanthodes is shown in Dr. 
Fritsch’s outline figure reproduced below. ‘The cartilages of the head 
are calcified with granulations, as in sharks; and there are splints 
covering the jaws, but neither these nor any other skeletal parts have 
the structure of bone. The roof of the skull is covered at least in 
part with small dermal plates, and there is a ring of plates round the 
eye. The gill-arches are so much crowded that Dr. Fritsch thinks 
the gill-slits must have been covered by a flap of skin, asin the existing 
Chimzroids. The notochord must have been persistent, and 
there are rarely traces of the neural and hemal arches above and 
below the vacant space it once occupied. The tail is heterocercal, 

Fic. 1.—Outline restoration of Acanthodes bronni; Permian, Rhenish Prussia. 
(After Fritsch.) 
the upper lobe being much produced; and in front of all the fins, 
except the caudal, there is a ‘strong spine. The body is covered with 
little quadrangular scales, consisting of dentine enamelled at the 
surface ; and the “ lateral line” does not pierce these scales, but runs 
between two series. 
Among the Permian Acanthodians Dr. Fritsch recognises three 
genera, one of which is destitute of pelvic fins. The large size of 
the paired fins, however, is one of the chief characteristics of 
Acanthodes itself; and, as pointed out by Professor Cope, there is 
more evidence of a continuous pair of lateral fin-folds in these Acan- 
thodians than in any other fishes. Some of the Devonian genera 
(e.g., Climatius), exhibit between the pectoral and pelvic fins a close 
and regular series of paired spines, in every respect identical with 
those supporting the fins themselves; and it is quite possible that 
these intermediate spines may also have been connected with fin- 
membrane. 
It is strange to find a group of fishes like the Acanthodians 
among the sharks—fishes which at the present day never exhibit 
structures of the nature of membrane-bones, and never have the 
