GENERAL STRUCTURE AND ORDERS. IO27 



Family Hyloplesionid^e. — This family is readily recognised by 

 the somewhat narrow head, the smooth cranial bones, and the en- 

 velopment of the whole body (fig. 955, a) in an armour of scutes. 

 The caudal ribs (fig. 955) are well developed. It comprises the 

 genera Hyloplesion, Seeleya (fig. 955), Ricnodon, and Orthocosta, from 

 the Permian of Bohemia. Hylonomns and Smilerpeton, from the 

 Carboniferous of Nova Scotia, are imperfectly known forms which 

 may belong to the same family, in which case the name Hylonomida 

 might be adopted. All the species are of small size. 



Family Microbrachid^e. — This family includes small slender 

 forms, with short pectoral limbs, strongly sculptured cranial bones, 

 and scutes covering the entire body. The type genus Microbrachis 

 occurs in the Permian of Bohemia, and has a long narrow skull. 

 Three species are known. Another representative of this family is 

 Tuditanus, of the Carboniferous of Ohio, characterised by its broad 

 and expanded skull. Cocytinus, of the same deposits, may be pro- 

 visionally placed in this family. 



Suborder 4. Labyrinthodontia Vera. — The genera included 

 in this group are characterised by their Crocodile-like bodies ; the 

 disk-like centra of the vertebrae, when these are fully ossified ; by 

 the vertebral column being, at least in the young, very generally of 

 the types known as rhachito7?ious and ei?ibolomerons ; by the teeth 

 being more or less folded ; and by the outer surface of the skull 

 bearing a more or less strongly-marked sculpture, frequently accom- 

 panied by the presence of the so-called mucous canals. Some 

 authorities divide this group into the Temnospondyli and Stereo- 

 spondyli, according to the incomplete or complete ossification of the 

 vertebral centra ; but Dr Fritsch regards the whole series as con- 

 stituting a single group — a view which is supported by the cir- 

 cumstance that in many of those forms in which the vertebrae are 

 fully ossified in the adult, in the young stage their ossification is 

 incomplete. 



Before proceeding further it will be advisable to briefly consider 

 the nature of the above-mentioned types of vertebral structure. In 

 certain genera like Diplospondylus 1 (Diplovertebron) and Cricotus 

 each caudal vertebra consists of an anterior centrum carrying the 

 neural arch, and a posterior intercentrum to which the chevrons are 

 united. These intercentra, according to the views of Professor Cope, 

 correspond with the chevron - bearing intercentra of Clepsydrops 

 among the Anomodont Reptilia, and the wedge -bones of Sphen- 

 odon among the Rhynchocephalians ; this type of structure being 

 known as the embolomerous. In the trunk vertebrae of other genera 

 like Trimerorhachis (fig. 957) and Archegosaurus each vertebra (fig. 



1 This name has been proposed in lieu of the hybrid Diplovertebron. 



