COMPENDIUM OF GENERIC DISTINCTIONS. 



635 



toothed. Antennae in two rows. Legs stout; third, fourth, and 

 fifth pairs out-toed. 



Genus. Paxdalus. — Outer antennae long, inner ending in two 

 many-jointed filaments. First pair of legs one-toed. Beak 

 turned up at tip, doubly toothed. Second pair of legs two-toed. 

 Many seas. 



Genus. Pai..emon. — Inner antennae with three filaments. 

 Second pair of legs strongest. Eyes large. Many seas. 



Genus. Hippoeyte. — Beak large and compressed. Inner 

 antennae tipped with two many-jointed filaments. Many seas. 



Family. PENiEIDiE. — Antennas in two rows, lower or both 

 pairs long. Beak long and compressed; abdomen also long and 

 compressed. 



Genus. Pen.eus. — Inner antennas short; first joint of upper 

 antenna? very large and excavated above, forming a socket for 

 the eyes. Carapace crested along the middle; a groove on each 

 side of the crest. Many seas. 



Genus. Pasiph.ea. — Carapace narrow in front, beak short, 

 not toothed. Basal joint of inner antenna; slender and with two 

 many-jointed threads. Abdomen lung; false legs of first ring 

 with a single plate, rest with two plates. Many seas. 



Order. STOMAPODA.— Gills external, formed of cylinders. 

 Seven or eight pairs of legs, mostly near the mouth. 



Family. MYSID.E.— Carapace with folded edges, thorax thick 

 and compressed at sides. Abdomen large; six to eight pairs of 

 legs on thorax, each with a large palpus, looking much like an- 

 other leg. 



Genus. Mtsis. — No gills on thorax. False feet of abdomen 

 very small, and without gill appendages. In females, branchial 

 appendages to last two pairs of feet very large. Many seas. 



Family. PHYLLOSOMIDJE. — Carapace flat, membranous, 

 transparent, formed of two bucklers. Feet small, mostly slen- 

 der. No scales at base of outer antennae. Abdomen small. 

 One genus. Atlantic and Eastern seas. 



Family. ERICHTHIDiE.— Carapace membranous, transpar- 

 ent, folded at sides, prolonged in front into a point. Eyes thick 

 and globular. 



Genus. Ericutiius. — First joint of eye-footstalks shorter than 

 second. Hinder angles of carapace shandy pointed. 



Family. SaTJILLID-E. — Body long. Carapace three-lobed. 

 First pair of thoracic legs very large, last joint folding upon its 

 predecessor. Second, third, and fourth pairs much smaller and 

 furnished with pincers; next three pairs slender and nearly 

 cylindrical. 



Genus. Squii.la. — Last three pairs of legs with long pointed 

 appendages, first joint of first pair of legs flat and deeply toothed 

 on the inner edge. Many seas. 



Sub-class. EDRIOPHTHALM ATA. — Eyes sessile; 

 body in three portions. Respiration through modified limbs. 



Order. AM PH I POD A. —Head formed of a single segment, 

 mandibles mostly with a palpus. Gill-vesicles under thorax; 

 first five pairs of abdominal limbs differ in form and used for 

 locomotion. 



Family. ORCHESTID.E. — Formed for leaping; body com- 

 pressed, no palpus on mandibles. Two short appendages to 

 tail. Upper antennae shorter than basal joints of lower an- 

 tennae. 



Genus. Talitrus. — First pair of legs simple, no pincers on 

 second pair. Lower antenna; long. Most seas. 



Genus. Orchestia. — First and second pairs of feet with 

 slight pincers. Jaw-feet blunt at tip. First pair of legs smaller 

 than second. Many seas. 



Family. GAMMARIDiE. — Formed for swimming, palpus on 

 mandibles. Antennae tipped with lash-like appendages. Legs 

 long. 



Genus. Kroyera.— Shell of head projecting like a hood and 

 pointed. Jaw-feet with well-developed pincers. Many seas. 



Genus. Sulcator. — Upper antennae half length of lower, 

 forked, with second joint flattened. Second and third pairs of 

 legs two-clawed. Most seas. 



Genus. Gammarus. — Upper antennae slender, small bristles 

 at base of fourth joint. Tufts of spines on tail. First and sec- 

 ond pairs of legs with slight pincers. Most seas. 



Family. COROPHIDJE.— Formed for walking. Body rather 

 flat, abdomen straight, all segmeus free. Palpus on mandibles. 

 Antennae-like legs. 



tic*, us. Cekapos. — No lash on antennas. Two of the toes 

 with two joints; animal inhabiting a tube. Many seas. 



Genus. Corophium. — Lower antennae very large and without 

 lash, first pair of legs with a lash. Body long, cylindrical, 

 rather compressed. Many seas. 



Family. CHELURID.ffi.— Two or three segments of abdomen 

 united. Antenme short and leg-like. Six points on tail. 



Genus. Chelura.— Upper antennae shorter than lower, and 

 with an appendage. Fourth to sixth segments fused together. 

 Many seas. 



Tribe. HTPEEITA.— 'HcuiX very large; mandibles also 

 large. First pair of jaws of three joints; thorax six or seven- 

 jointed. Some legs prehensile; end of abdomen for swimming. 



Family. PHRONIMADJE. Second pair of antenna; stiff and 

 bristle-like; some of true legs prehensile. 



Genus. Phroxima.— Head vertical; tail ending in thread- 

 like appendages. Body soft, semi-transparent. Fifth pair of 

 legs largest, and with pincers. Many seas. 



Genus. Metiecus. — Two first pairs of legs shortest, and with 

 small pincers. Many seas. 



Order. L^EMODIPODA. -Abdomen very small, hardly visi- 

 ble. Body cylindrical, or depressed. Head very small. 



Family. CYAMIDJE. — Body depressed, oval. Eyes com- 

 pound. Antennas close at base. Five pairs of legs, all pre- 

 hensile. Respiratory apparatus on second and third joints of 

 thorax. 



Genus. Cyamus. — Head small, fused into first segment of 

 thorax. Many seas. 



Order. ISOPODA.— Body depressed, abdomen large. Mostly 

 fourteen legs, and in the females the greater number have a 

 large horny plate. Several segments of abdomen fused to- 

 gether. 



Family. ID0TEID.2E.— Appendages of last false legs very 

 large and flat, covering all under side of abdomen. First seg- 

 ment very large and shield-like. 



Genus. Arcturus.— Body long. Three last pairs of legs used 

 for walking; four first pairs flat at tips. Antennae leg-like. 

 Northern seas. 



Family. ASELLIDJE.— Body long. First pair of antennae 

 very small. Abdomen jointed, last joint large and shield-like; 

 tip of abdomen with pointed appendages. 



Genus. Limnoria. — Body capable of being curled up. Eyes 

 distinct. Antenna; in pairs, one pair over the other. Tail of 

 many segments. Many seas. 



Genus. Asellus.— Front legs largest. Body oblong, flat- 

 tened, nine-jointed; one joint for the head, seven for the thorax, 

 and one for the abdomen. Tail appendages long. Fresh 

 waters. 



Family. ONISCIDJE.— One pair of antennas. Abdomen of 

 six segments, last rather small. Legs slender. 



Genus. Ligia. — Outer antennae with last joint compound. 

 Four appendages to tail, two on each side. 



Genus. ONISCUS. — Antenna; eight-jointed, base hidden by 

 projecting front of head. Tail appendages four-jointed. 



