566 The Holocephali, or Chimasras 



ture resembles that seen in the deep-sea shark, Mitsukurina, 

 and in Polyodon. In Rhinochimazra pacifica of Japan the teeth 

 in each jaw form but a single plate. In Harriotta raleighana, 

 of the Gulf Stream, they are more nearly as in Chinuzra. Both 

 are bathybial fishes, soft in texture, and found in great depths. 

 The family of Callorhynchida, or Antarctic Chimasras, includes 

 the bottle-nosed Chimaera (Callorhynchus callorhynchus} of the 

 Patagonian region. In this species the snout is also produced, 

 a portion being turned backward below in front of the mouth, 

 forming a sensory pad well supplied with nerves. 



Extinct Chimaeroids. According to Woodward, three other 

 families are recognizable among the extinct forms. 



The Ptyctodontidcz are known from the teeth only, a single 

 pair of large, laterally compressed dental plates in each jaw, 

 with a few hard tritoral areas. These occur in Silurian and 

 Devonian rocks. Ptyctodus obliquus from the Devonian of 

 Russia is the best-known species. Other genera are Rhyn- 

 chodus and Palceomylus. 



The SqualorajidcB have the head depressed and the snout 

 produced in a flat rostrum, as in Harriotta. There is no dorsal 

 spine, and the teeth are a few thin curved plates. The frontal 

 holder of the male is well developed. The few species occur in 

 the Lias. Squaloraja dolichognathos is known from numerous 

 fragments from the Triassic in England and Scotland. Chalcodus 

 permianus is found in German Permian. 



The Myriacanthidcs have the body elongate, with dermal 

 plates on the head and a long straight spine in the dorsal fin. 

 The frontal holder is large. The species, few in number, are 

 found in Mesozoic rocks. Myriacanthus paradoxus is the best- 

 known species. Of another species, Chim&ropsis paradoxa, 

 a skeleton about three feet long has been found which shows 

 a number of peculiar traits. The skin is covered with ribbed 

 shagreen scales. The dorsal fin has a large spine with retrorse 

 serrations behind. The tail is slim, and the pectoral and ven- 

 tral fins are very large. Bony plates with conical spines protect 

 the neck. The teeth are large and angular, of peculiar form. 



Ichthyodorulites. The term ichthyodorulite (ix^vs, fish ; $ opv, 

 lance; A/6*o?, stone) is applied to detached fin-spines, dermal 

 spines, and tubercles belonging to unrecognized species of 



