584 BULLETIN 54, UNITED STATES NATIONAL MUSEUM. 



d. Maxillipeds with terminal joints small and almost rudimentary, hardly 



longer than masticatory lobe, which is truncate. 



e. External antenna; generally long, close together, with antennal openings 

 large. Body as a rule scarcely able to be contracted in a ball. Head 

 less manifestly immersed in first thoracic segment. Lateral parts of the 

 head separated by a vertical marginal and inframarginal line. Clypeus 

 arched. Legs generally long. Uropoda produced, reaching beyond 

 the terminal segment of the abdomen and the preceding segment. 

 Terminal segment narrower than preceding ones and usually conically 



produced at end Family XXV. ONISCIIX*: 



ef. External antennae generally short, with antennal openings small. Body 

 able to be contracted into a ball. Head immersed in first thoracic 

 segment. Lateral parts of the head undifferentiated. Clypeus perpen- 

 dicular. Legs generally short. Uropoda short, not reaching beyond 

 the terminal segment of the abdomen or the preceding segment. 

 Terminal segment short and broad... Family XXVI. ARMADILLIDID^E 

 d'. Maxillipeds with terminal joints large, lamellar, much longer than masti- 

 catory lobe, which is acutely produced Family XXVII. SCYPHACID^E 



c f . Buccal mass prominent. First maxillae have three plumose set* on the 

 inner plate. Mandibles with molar expansion large and broad, exhibiting 

 a finely fluted triturating surface. 



d. Head without any lateral lobes, frontal part rounded. Eyes well developed 

 or wanting. Inner antennae with last joint very small and without dis- 

 tinctly developed sensory filaments. Second antennae with flagellum 

 multiarticulate. Posterior maxillae with two thick, hairy bristles. Max- 

 illipeds with the terminal part distinctly five-articulate, masticatory lobe 

 truncate at tip, epignath short. External sexual appendages in male 

 double. Inner branches of first pair of pleopoda of a similar structure 

 in both sexes, that of second pair in male terminating in long stylet. 



Both branches of uropoda styliform Family XXVIII. LIGYDID.E 



d' ' . Head with distinct, though not very large, lateral lobes, front more or less 

 produced. Eyes small or wanting. Inner antennae with last joint well 

 developed and tipped with a number of delicate sensory filaments. Sec- 

 ond antennae with flagellum not more than six jointed. Posterior 

 maxillae without any bristles. Maxillipeds with the terminal part gen- 

 erally imperfectly articulated, masticatory lobe terminating in a thin lash, 

 lepignath narrow, linguiform. Sexual appendage of male simple; inner 

 branch of both first and second pairs of pleopoda modified. Uropoda 

 with branches conically tapered Family XXIX. TRICHONISCID.E 



Family XXIII. TYLID^. 



Inner lobe of the First maxillse furnished with three subequal 

 plumose processes. 



First pair of antennas small, composed of one or two articles. 

 Abdomen composed of six distinct segments. 



Four pairs of pleopoda present; the first pair of pleopoda are want- 

 ing; the pleopoda of the second, third, fourth, and fifth segments have 

 single branches, all branchial ; the branch of the second segment, how- 

 ever, in the male is produced on the inside in a long, compressed stylet. 



The uropoda form an operculum, with the outer branch very small 

 and situated at the apex. 



See Budde-Lund for characters of family, Crustacea Isopoda Terrestria, 1885, 

 p. 272. 



