104 Alexander Petrunkcviich, 



to the patella of spiders, with this difference, however, that it is 

 the distal end of the trochanter. 



Specimen in the Daniels collection. Plate IX, figs. 49, 50 ; text 

 figs. 60, 61. Total length 16.5 mm. Cephalothorax 7.0 mm. long, 

 its probable width 5.1 mm. It has a distinct triangular shape, 

 and together with the abdomen and lims, represents the moidd 

 of the actual specimen. This interpretation may seem strange to 

 one who examines the obverse alone, since the specimen on the 

 obverse stands out bodily to a considerable height and gives the im- 

 pression of a petrified specimen. But a comparison with the reverse 

 of the same specimen shows at once what has happened to this 

 as to the other two specimens. Under pressure of the drying mud 

 the dorsal surface of the abdomen of the specimen caught in it was 

 pressed in until it became concave instead of remaining convex, 

 coming in contact with the ventral surface. Why this happened 

 to the dorsal surface and not to the ventral one, is not clear, but 

 presumably the dorsal surface was less chitinized and therefore 

 softer. The cephalothorax being much harder, kept more or less 

 its shape, and what appears on it as the median crest was in rea- 

 lity a deep groove. The irregular, polygonal depressions appearing 

 as such both on the abdomen and cephalothorax were e\ndently 

 thickened areas of the chitin and formed in life low elevations. 

 The abdomen covers in the specimen the posterior edge of the 

 cephalothorax. Consequently we may assume that it had in life 

 a segment anterior to the first visible tergite, consequenth', if the 

 anal operculum represents the last tergite the abdomen must have 

 been composed of eleven segments as in Anthracomartus. The plate 

 surrounding the anal operculum represents the fused tergite and 

 sternite of the tenth segment and since in front of this plate may 

 be counted only seven sternites, the first visible sternite which 

 has the shape of a triangle correponds to the first, second and third 

 abdominal segments. The dorsal surface of the abdomen was 

 a little displaced laterally and shows on the left the sternites. Bear- 

 ing all tliis in mind we may give the following description of the 

 specimen as it must have appeared in life. 



Cephalothorax triangular, high, covered with irregular poly- 

 gonal thickenings. A deep transverse groove in the middle, another 

 a little in front of it and a third close to the posterior margin wliich 

 is covered by the abdomen. Two almost parallel grooves run from 

 the anterior t ansverse groove to the anterior end of the cephalo- 

 thorax. Two oblique ridges run from the sides of the anterior 

 groove backward uniting a little in front of the median transverse 



