ISOPODS OF NORTH AMERICA. 



17 



The first three free segments of the thorax are subequal; taken 

 together, somewhat shorter than the head and twice as long as the 

 fourth free segment. 



All the segments of the abdomen are pres- 

 ent and visible. The last segment is taper- 

 ing, widely rounded, and more than twice 

 as wide as long. 



The first pair of legs are robust; the 

 chelae are more than half as short as the 

 head; the fingers are a little shorter than the 

 hand, the thumb serrate almost to the apex. 

 The ambulatory legs are all subequal, slen- 

 der. The pleopoda are very short, and fur- 

 nished with a few short setae. 



The uropoda are very short, double- 

 branched, both branches being composed of 

 two articles, the inner branch being twice 

 as long as the outer branch, and stouter. 



The marsupium is composed of two large 

 lamellae issuing from the base of the fifth 

 pair of legs. a 



FIG. 20. CRYPTOCOPE ARCTIC A 

 (AFTER HANSEN). a, ANTENNAE 



OF FEMALE, b, UKOPOD OF FE- 

 MALE, c, UROPOD OF MALE, d, 

 ANTERIOR PART OF BODY OF 

 MALE. (ENLARGED.) 



4. Genus LEPTOGNATHIA Sars.& 



Eyes wanting. Pleopods in female small and sometimes wanting; 

 those in male well developed. Abdomen composed of six segments. 

 Uropoda usually biramous, sometimes apparently simple, the outer 



a The above description is adapted from the following description of Hansen's: 

 Femina. Corpus subcylindricum, circiter quadruple et dimidio longius quam 

 latius. Scutum -cephalothoracicum ad f rontem versus sensim angustatum, margine 

 anteriore aliquantum producto et apice obtuso. Segmenta tria libera anteriora inter 

 se subaequalia, simul sumpta scuto cephalothoracico aliquanto breviora et segmento 

 quarto libero duplo longiora. Segmenta caudae omnia manifesta; segmentum ulti- 

 fnum declive et valde rotundatum, plus duplo latius quam longius. Oculi nulli. 

 Antennas primi paris quadriarticulatae, anguste conicae; scuto cephalothoracico quarta 

 parte breviores; articulus basalis duas quintas partes antennae explens, a latere visus 

 cylindricus, pronus ad basin versus sensim incrassatus; articulus secundus articulo 

 tertio plus quam dimidio longior et articulo quarto nonnihil brevior; articulus uterque 

 seta in angulo exteriore apicali instructus; apex articuli quarti setis compluribus 

 longis ornatus. Antennae secundi paris tenues, quinque-articulatae, antennis primi 

 paris nonnihil breviores. Pedes primi paris (chelipedes) robusti; chela scuto ceph- 

 alothoracico plus quam dimidio brevior; digiti manu paulo breviores, pollice prope 

 apicem serrato. Pedes gressorii omnes inter se subaequales, tenues. Pleopoda bre- 

 vissima, setis nonnullis brevioribus instructa. Uropoda brevissima, biramea, ramis 

 ambobus biarticulatis, ramo interno quam externo duplo longiore et crassiore. Mar- 

 supium e laminis duabus magnis, ad pedes quinti paris affixis, formatum est. Long. 

 1.67 mm. HANSEN, Dijmphna-Togt. zool.-bot. Udb., 1887, p. 209. 

 b See Sars for characters of genus. 

 2858905 2 



