NEW SUBORDER AND NEW SPECIES OF PHYTOSAURUS 527 



small plate of irregular form such as occurs on the lower part of 

 the body of the Parasuchia was found with the specimen but its 

 position is uncertain. 



The dorsal armor is most conveniently described as a series of 

 transverse arches. The first five are not metamerically arranged 

 with relation to the vertebrae; they cover the first ten vertebrae, 

 rather more than the whole cervical series; posterior to this the 

 plates correspond in number and position with the vertebral seg- 

 ments below. Each arch consists of a pair of median plates with a 

 low blunt spine or knob, and a pair of outer plates which carry 

 spines of varying size and form. The plates of the first five arches 

 have only a slight sculpture, those posterior to the fifth have an 

 increasingly heavy sculpture of pits and ridges which soon becomes 

 very coarse. The form of the various plates is shown in Figure 4, 

 which is a semi-diagrammatic restoration of the dorsal armor. 

 Except for the three posterior dorsal arches and the median caudals 

 there is evidence for all the parts. The arrangement of the 

 plates is such as is dictated by the form and characters of the 

 units, none having been found in sequence posterior to the cervical 

 region. 



The first five arches show a gradual increase in the size of 

 median plates and a rapid increase in the size of the spines upon 

 the lateral plates. In the fourth arch the median and lateral 

 plates of the right side are co-ossified and in the fifth arch the 

 median plates of both sides and the lateral plate of the left side 

 fit well together; in these arches there can be no doubt of the 

 position and direction of the spines and by analogy with these 

 the position of the other plates and spines is determinable. The 

 fifth arch is most astonishing in the development of the relatively 

 enormous spines which extend outward almost horizontally and 

 curve forward over the third and fourth arches. In all of the 

 arches of the cervical region the plates are thickened at the point 

 of juncture in the same arch and thinned anteriorly and posteriorly 

 to permit of the overlapping from before backward and allow for 

 slight vertical movement of the head and neck; any lateral move- 

 ment, as indicated by the form of the plates and the faces of the 

 vertebral centra, must have been very slight. 



