144 NEW YORK STATE MUSEUM 



outline, which have been found as yet only in the detached condition, but 



evidently represent the median ventrals of some large member of the family. 



One such, having a length of 29 cm, and maximum width of 12.5 cm, has 



been figured by the present writer in the bulletin of Museum of Comparative 



Zoology [31 : 26, pi. 5, fig. i]. It is abruptly truncated in front, and bears 



traces of overlap by contiguous plates ; accordingly if this plate is rightly 



interpreted as belonging to Titanichthys, there is excellent reason to 



suppose that the ventral armor consisted of the same number of plates as 



in Dinichthys. 



Genus pbotitanichthys nobis 



Primitive Coccosteans of small size, displaying composite characters of 



later forms. Arrangement of cranial plates in general resembling that of 



Coccosteus, the centrals meeting in a sinuous longitudinal suture and not in 



contact with the pineal ; the latter is subellipitical in outline, its long axis 



directed transversely, and pierced by a relatively large pineal foramen ; 



rostral plate also very broad. External surface finely tuberculated ; lateral 



margin of head shield apparently not much widened posteriorly ; sensory 



canals distinct [dentition unknown]. 



Protitanichthys fossatus sp. nov. 



Plate 10, figure 2 ; text figure 30 



The unique specimen which is here made the type of a new genus and 

 species is of interest in two respects ; first, on account of its geological 

 antiquity, and in the second place, because it displays synthetic characters. 

 In the majority of its features, a close approximation is to be observed to 

 Coccosteus, and to the more primitive species of Dinichthys, as for example, 

 D. halmodeus. First of all, there is to be noted its small size, corre- 

 lated with finely tuberculate ornament of the external surface ; secondly, 

 the sinuous suture line between the pair of central plates ; and thirdly, the 

 exclusion of the pineal from contact with the latter pair. The form of the 

 head shield, too, although this can only be determined approximately, 

 appears to have been long and narrow, without much lateral expansion at 

 the posterior border. One striking peculiarity, however, distinguishes it 



