562 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.xxiii. 



c. Terminal segment of body conicall y produced. Basal joint of uropoda oblong. 

 Inner branches not contiguous along their inner lateral margins. 



60. Oniscus. 



(•'. Terminal segment of body short, widely rounded posteriorly. Basal joint of 



uropoda broadly expanded inside. Inner branches contiguous along their 



inner lateral margins 61. Synurojms, new genus. 



t/. Epimera of thoracic segments small. Abdomen abruptly narrower than tho- 

 rax; first two segments generally equal in length to those following; 



epimera very small, but manifest 62. Fhiluscki. 



a' . External opercular ramus of the first and second pairs of abdominal appendages 

 furnished with tracheae. 

 h. Flagellum of external antennae biarticulate. 

 V. Abdomen not abruptly narrower than thorax. Epimera of abdominal seg- 

 ments large. 

 d. Body very convex, callable of being rolled up into a perfect ball. Articles 

 of flagellum of external antennae subequal. Last abdominal segment 

 reaching very little beyond the epimera of the preceding segment. Ex- 

 ternal branches of the uropoda equal in both sexes. External opercular 

 ramus of all the abdominal appendages furnished with tracheae. 



63. Oylisticus. 

 d'. Body more or less depressed, with lateral j^arts lamellarly expanded. 

 Articles of flagellmn of external antennae with the first article generally 

 longer than the second, often subequal, or even a little shorter. Last 

 abdominal segment generally not reaching beyond the epimera of the 

 preceding segment. External branches of the uropoda longer in the male 

 than in the female. External opercular ramus of the first and second 

 pairs of abdominal appendages, and m some species of all the pairs, fur- 

 nished with tracheae 64. Forcellio. 



<••'. Abdomen abruptly narrower than thorax. Epimera of abdominal segments 

 small. 

 d. First article of flagellum of external antennae generally longer than second. 

 Last abdominal segment reaches sufficiently beyond the epimera of the 

 preceding segment. External opercular ramus of the first and second 

 pairs of abdominal appendages, rarely of the third or of all the pairs, fur- 

 nished with tracheae 65. Metoponorthus. 



d\ Flagellum of external antennae with the first article shorter than the 

 second. Last abdominal segment reaches much beyond the epimera of 

 the precedmg segment. External opercular ramus of the first and second 



pairs of abdominal appendages fiu-nished with tracheae 66. Rhyscotus. 



f/. Flagellum of external antennae quadri-articulate 67. Acanthoniscus. 



60. ONISCUS Linnseus. 



ANALYTICAL KEY TO THE SPECIES OK OXISCUS. 



a. Caudal segment a little shorter than inner branches of the uropoda. 



139. Oniscus asel/us LinuK^UH. 

 o'. Caudal segment exactly equal to the inner Ijranch of the uropoda. 



140. Oniscuif uffinis Say. 



139. ONISCUS ASELLUS Linnaeus. 



Oniscus asellus Lixx^Ers, Fauna Suecica, 2d ed, p. 500. 



Oniscus tnurarius Cuvier, Jour. Hist. Nat., II, p. 23, pi. xxvi, figs. 11-13. — 



BuDDE-LuND, Crust. Isop. Terrestria, 1885, pp. 202-204. 

 Oniscus asellus G. O. Sars, Crust, of Norway, II, Pts. 9, 10, 1897, p. 171, 172^.. 



