120 



Alexander Pctriinkevitch, 



reproduced on i)late XII, fig. j^. Both specimens of the University 

 of Chicago are in an excellent state of preservation. Specimen 

 No. 9233 is reproduced on plate XIII, fig. 76 and 77. It shows only 

 few traces of the anterior tergites superimposed over the sternites, 

 especially visible on the right edge of the abdomen. Specimen 

 No. 9234 is reproduced on plate XII, fig. 75. The apparently larger 

 width of its abdomen is due to greater flattening under pressure of the 

 drying mud, and consequently both surfaces 

 are clearly superimposed. This specimen mea- 

 sures 24.0 mm. The best preserved specimen 

 is the one in the Peabody Museum, No. 185, 

 reproduced on plate XIII, figs. 78, 79. Un- 

 fortunately the photographs did not come out 

 as well as they should. This specimen was 

 very little compressed dorsoventrally ; conse- 

 quently the obverse shows only the dorsal sur- 

 face, while on the revers eare visible the im- 

 pressions of the abdominal anterior tergites 

 on the sides only of the abdomen. Omitting 

 further discussion of other specimens I shall 

 now give a detailed description of the last 

 mentioned. 



Specimen No. 185 of the Peabody Museum. 

 Total length 21.75 mm. Cephalothorax 12.7 

 mm. long in middle line, 9.1 mm. wide. It 

 has rounded latero-posterior corners and is 

 posteriorly produced into a median lobe \\\\.\v 

 rounded end and concave sides. Anteriorly 

 the cephalothorax forms a sharp spine-like pro- 

 jection. The cephalothorax is high, sloping 

 gradually to the sides and front. Two small, 

 round eyes, 3.25 mm. from anterior end, about double their diameter 

 apart. The posterior lobe of the cephalothorax reaches as far as 

 the anterior edge of the third tergite. It is impossible to decide 

 whether the first and second tergites are each composed of two scle- 

 rites, or whether the lobe of the cephalothorax merely covers the 

 short median part of these tergites. The following four tergites 

 are short, but with more or less parallel procurved edges. The 

 posterior edge of all six tergites is heavily thickened and appears 

 in the specimen as a deep groove. The demarcation lines between 

 the following four tergites are also clearly visible, but appear in the 

 specimen as narrow, low ridges, which proves that the edge of these 



Fig. ■jg. — Architar- 

 bus rotimdatus Scud- 

 der, specimenNo. 1 85 

 of the Peabody Mu- 

 seum ; dorsal surface 

 of cephalothorax 

 and abdomen. X ~ 



