448 SAMUEL H. SCUDDER ON THE 



stout and tolerabl}^ long. Abdomen oval, considei-ably consti'icted at the base, com- 

 posed of nine segments, of which five of the basal ones are very narrow, at least on the 

 under surface, but transverse and not angulate, the remainder longer and subequal or 

 lengthening posteriorly. 



This genus is so far known only from America by two very distinct species, both de- 

 sci'ibed below. It is possibly nearly related to Eotarbus KuSta from the Bohemian coal. 



Geratarbus lacoei sp. nov. 

 PI. 40, fig. 11. ' 



The ccphalothorax is neai'ly orbicular and the wedge-shaped pcdigerous segments 

 subequal; the posterior border shows a weak, broad, and rounded emargination. Only 

 the very base of the first pair of legs can be seen; of the others on one side or the other 

 three or four joints each; in the two middle pairs the first three joints are subequal, 

 about half as long again as broad, flattened and a little arcuate, the anterior edge 

 produced at tip and base, so as to form by the union of the adjacent joints a decided den- 

 tifoi-m spine directed forward and outward, and more distinct on the second than on the 

 third pair of legs, both of which curve forward; the last pair of legs is directed backward 

 and is differently constructed, having no such compound tooth, though both outer and 

 inner apices are slightly produced and rounded; the first joint is scarcely longer than 

 broad, the second and thii'd subequal and nearly twice as long as broad, all of similar 

 breadth to those of the other legs. 



The abdomen broadens rapidly from its base over the two basal segments until it is 

 nearly a third broader than the thorax, then tapers, at first gently, afterwards rapidly, 

 with a well rounded extremity, the whole only a little longer than the greatest breadth ; 

 all the joints are transverse, the first five very short, the sixth twice as long, the eighth 

 three times as long, the seventh midway in length between these, and the last nearly 

 equal in length to the preceding two. The lateral sulcus is distinct but not deep, sep- 

 arating a very narrow side piece from the main body of the abdomen. 



The whole body is rather finely and uniformly punctate, the legs much more coarsely 

 and distinctly. 



Length of body, 11 mm. ; ccphalothorax, 4.8 mm.; abdomen, 6.2 mm.; breadth of thorax 

 4 mm.; abdomen, 6 mm.; length of second joint of second pair of legs, 1.3 mm.; of third 

 pair, 1.5 mm.; of fourth pair, 1.8 mm.; breadth of last, 1.2 mm. 



Mazon Creek, 111. Mr. E. D. Lacoe, ISTo. 1765ab. 



Geratarbus scabrum sp. nov. 

 PI. 39, fig. 5. 



Ccphalothorax apparently orbicular but for its truncate hinder extremity, but in the 

 specimen turned a little so that the median line is thrown (as seen in the figure) to the 

 left. The upper surface appears to be exposed so that the form of the subordinate parts 

 can scarcely be seen. Fragments of the legs are preserved, showing parts of cvcn-y pair 

 but the first; all are flattened; the basal joints of the second and third pairs are more 



