ANTHRACOSIRO. 69 



Family AnthracosjronidjTC, Pocock. 

 1903. Anthracosironidse, E. I. Pocock, G-eol. Mag. [4], vol. x, p. 408. 



Carapace of prosoma with only a single posterior transverse sulcus ; elevated in 

 the middle and sloped anteriorly, laterally and posteriorly to the borders, thus 

 resembling in a general way that of the Anthracomartidas. Opisthosoma with the 

 pleural laminaa smaller than in that family and undivided, those on the anterior terga 

 being very small. Anterior sterna of this region, at least in Trir/onotarbus, small 

 and crowded together, not enlarged, and posteriorly produced, the first triangular 

 and wedged between the coxas of the last pair of appendages, the following two or 

 three short and not laterally impressed ; the posterior border of the posterior sterna 

 evenly convex, not mesially angled or notched. 



This family constitutes in some respects an interesting connection between the 



Anthracomartida3 and the Eophrynidaa, resembling the former in the structure of 



the carapace and the latter in the shape and size of the anterior sterna of the 



opisthosoma. 



The two genera referred to the AnthracosironidaB may be distinguished as 

 follows : 



a. Carapace rounded or truncated in front, its lateral borders only markedly converging 

 in front of the middle ; all the pleural laminae directed obliquely backwards, their 

 anterior and posterior borders forming distinct angles with the corresponding 

 borders of the median area of the terga that bear them . . Anthracosiro. 



a . Carapace markedly narrowed and angular in front, its lateral borders strongly con- 

 verging forwards from a point behind the middle ; the anterior and posterior borders 

 of the pleural lamina? following the lines of the corresponding borders of the median 

 area of the terga ....... Trigonotarbus. 



Genus ANTHRACOSIRO, Pocock. 



1903. Anthracosiro, R. I. Pocock, Geol. Mag. [4], vol. x, pp. 247-250 and 405—407. 



1904. Anthracosiro, A. Fritsch, Palseoz. Araclm., p. 42. 



Generic Characters. — Carapace high, convex from before backwards, and from 

 side to side ; its median area widely, but not deeply, excavated longitudinally, and 

 defined by a ridge on each side, externally to which the surface slopes downwards 

 to the lateral margin at an angle of about 45 degrees ; the anterior portion of 

 the upper surface bearing a pair of widely separated tubercles, probably oculi- 

 ferous, or a transverse ridge at the ends of which eyes were probably situated ; 

 the lateral border strongly or slightly convex ; the anterior border convex or 

 nearly straight; the posterior border straight; a short area in front of the 

 posterior border defined by a transverse groove. The opisthosoma with seven 



