Scudder.] 296 [January 23, 



right mandible; this part has been removed on the opposite side to show the base 

 of the left maxilla, c. cardo, p. stipes, t. Tongue; I. p. labial palpus. 



Fig. 5. View of the base of the right fork,/., and its attachments seen from in 

 front, m. The extensor muscle of the fork, and lig. its ligament; mx., base of 

 galea, p. stipes. 



Fig. 6. View of same from behind, letters as in preceding figure, and c, cardo; 

 memb., elastic membrane connecting the fork with the lining of the mouth. 

 lb. Labium. 



The flexor muscles (mm.) of the stipes and galea are also seen, passing over the 

 base of the fork. 



Fig. 7. Galea and fork. m. Extensor muscle seen in the two previous figures ; 

 m 1 and m 2 , other muscles inserted on the base of the fork, their outer attachments 

 broken away ; lie/, ligament. (From another species of Psocus from Beverly.) 



Fig. 8. Shows the muscles of the mandible with their attachments ; /. m., flexor, 

 and 6. m., extensor, m. Molar surface of mandible. 



Fig. 9. Transverse section of clypeus. cl. Clypeus, and c. m. its contained mus- 

 cular bands with their tendons, t, attached to the oesophageal bone, ce. b., on either 

 side. ce. Space through which the oesophagus passes. I. m. Sections of the labial 

 muscles, seen in fig. 2. 



Fig. 10. Subcesophageal bone from in front. I. d. Duct of the lingual gland. 



Figs. 11-13. Anatomy of Atropos. 



Fig. 11. Labium and maxillary palpus. 



Fig. 12. Lingual glands, oesophageal bone, and the fork. 



Fig. 13. Eyes of Atropos. 



Rhachura, a New Genus of Fossil Crustacea. By Samuel 

 H. Scudder. 



Mr. William Gurley has recently sent me from the black limestone 

 of Danville, 111., a curious crustacean, allied to Dithyrocaris, con- 

 tained in a large kidney-shaped concretion. There are two separate 

 fragments, one partially overlapping the other; one is more conspic- 

 uous than the other, consisting of the last three segments of an 

 abdomen with a pair of lateral posterior appendages, all of a dull 

 clay-color; while the other scarcely differs in color from the matrix, 

 being only the impression of a portion of a carapace, the edge of 

 which partially overlies one of the caudal appendages of the first 

 mentioned fragment. Were it not for its caudal appendages the 

 latter would resemble in a remarkable manner the thorax and abdo- 

 men of an insect, completely covered by its wings; for so closely do 

 the lines of ornamentation upon the penultimate and antepenulti- 

 mate segments resemble the veins of an insect's wings, that for a 

 long time I was inclined to consider them such, notwithstanding the 

 anomaly of the large exarticulate abdominal appendages. That it 

 should be found in the same nodule with the carapace of a fluviatile 

 or marine crustacean, seemed no more remarkable than the assem- 



