100 



Alexander Petrunkcvitch, 



A nthracomartus trilohitus Scudder. 



Plate XI, fig. 60, text fig. 57. 



A. trilohitus Scudder, Proc. Amer. Acad. Arts Sci., Vol. XX, 



1884, p. 17. Id., C. R. Soc. Ent. Belgique, (3), 1885, p. 85, with 



fig. Id., Mem. Boston Soc. Nat. Hist., Vol. IV, 1890, p. 451, 



pi. 39, figs. 7-10. 



Altogether twenty-two specimens, all from the same locality. 

 Of these eighteen in the U. S. National Museum and four, including 

 the type. No. 136, in the Museum of 

 Comparative Zoology at Harvard Uni- 

 versity. None of the specimens shows 

 either the ventral surface or legs, so that 

 our knowledge of the species is based 

 entirely on the characters of the cephalo- 

 thorax and the dorsal surface of the ab- 

 domen. All are on dark grey carbon- 

 aceous shale, together with ferns. Al- 

 though their size differs, all specimens 

 have the same structure and same pro- 

 portions. All appear punctate or granu- 

 late. As for the anal operculum, it must 

 be stated that it is missing in some of 

 the specimens and present in others, 

 thus giving confirmation to the assump- 

 tion, that it was pressed through the 

 body from the ventral to the dorsal sur- 

 face. The posterior edge of the cephalo- 

 thorax is always strongly procurved. 

 Behind it is the first abdominal tergite, 

 partly covered by the cephalothorax and 

 devoid of pleural laminae. The anal 

 operculum appears perfectly round, imprinted on the eighth ab- 

 dominal tergite. Measurements of type specimen : cephalothorax, 

 5.25 mm. long; 7.5 mm. wide; total length, 15.0 mm. 



Specimen No. 1753 d of the Lacoe collection in the U. S. National 

 Museum. Length of cephalothorax in median line, 4.0 mm. ; width, 

 6.5 mm. Length of abdomen in median line, 9.3 mm. ; width in 

 the region of the sixth tergite, 8,3 mm. 



Found in the Upper Pottsville series, near Fayetteville, Wa- 

 shington County, Arkansas. 



Figure 5 7. — J nthracomar- 

 tus trilohitus Scudder, from 

 the Pennsylvanic (Upper 

 Pottsville) near Fayette- 

 ville, Arkansas, U. S. N. M. 

 No. 1753 d (Lacoe collec- 

 tion). X y 



