79 6 



COMPENDIUM OF GENERIC DISTINCTIONS. 



Family. ALPHEIDyE. Antennae in two rows, nine above. 

 Beak small and flat ; three last pairs with one claw. 



Genus. ALPHHUS. Carapace projecting like a hood ; beak 

 small or absent. Claw-legs large ; unequal. First and second 

 pairs of legs two-toed; third, fourth, and fifth, one-toed. 

 Many seas. 



Genus. ATHANAS. Beak small, not toothed. Three fila- 

 ments on inner antennae. First pair of legs large, powerful- 

 and unequal ; pincers thick. Eyes not prominent, but project- 

 ing beyond carapace. Many seas. 



Family. PAL^MONID^E. Beak long, compressed, and 

 toothed. Antenna: in two rows. Legs stout ; third, fourth, 

 and fifth pairs one-toed. 



Genus. PANDAI.US. 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_*MOX. Inner antennas with three filaments. 

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



Genus. HIPPOLYTB. Beak large and compressed. Inner 

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



Family. PENjEID^E. Antennae in two rows, lower or 

 both pairs long. Beak long and compressed ; abdomen also 

 long and compressed. 



Genus. PENVEUS. Inner antennae 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 antennae slender and with 

 two many-jointed threads. Abdomen long : false legs of first 

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



Order. STOMAPODA. Gills external, formed of cylin- 

 ders. 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 another leg. 



Genus. MYSIS. 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. PHYLLOSOMID^E. Carapace flat, membra- 

 nous, transparent, formed of two bucklers. Feet small, mostly 

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

 One genus. Atlantic and Eastern seas. 



Family. ERICHTHID.'E. Carapace membranous, trans- 

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

 thick and globular. 



Genus. ERICHTHUS. First joint of eye-footstalks shorter 

 than second. Hinder angles of carapace sharply pointed. 



Family. SQUILLID^E. Body long. Carapace three- 

 bed. First pair of thoracic legs very large, last joint folding 

 upon its predecessor. Second, third, and fourth pairs mucn 



smaller and furnished with pincers ; next three pairs slender 

 and nearly cylindrical. 



Genus. SQUILLA. Last three pairs of legs with long pointed 

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

 on th inner edge. Many seas. 



Sub-class. EDRIOPHTHALMATA. Eyes sessile; body 

 in three portions. Respiration through modified limbs. 



Order. AMPHIPODA. Head formed of a single seg- 

 ment, 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 

 compressed, no palpus on mandibles. Two short appendages 

 to tail. Upper antennae shorter than basal joints of lower 

 antennae. 



Genus. TALITRUS. First pair of legs simple, no pincers 

 on second pair. Lower antennae 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. GAMMARID/E. Formed for swimming, palpus 

 on mandibles. Antennae tipped with lash-like appendage*. 

 Legs long. 



Genus. KROYERA. Shell of head projecting like a hood 

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

 seas. 



Genus. SULCATOR. Upper antenna; 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 

 second pairs of legs with slight pincers. Most seas. 



Family. COROPHID^. Formed for walking. Body 

 rather flat, abdomen straight, all segments free. Palpus on 

 mandibles. Antennae-like Tegs. 



Genus. CERA PUS. No lash on antennae. Two of the toes 

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



Genus. COROPHIUM. Lower antennae very large and with- 

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

 rather compressed. Many seas. 



Family. CHELURID^E. Two or three segments of ab- 

 domen united. Antennae 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. HYPE RITA . Head very large; mandibles also 

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

 jointed. Some legs prehensile; end of abdomen for swim- 

 ming. 



Family. PHRONIMADiE. Second pair of antennse stiff 

 and bristle-like ; some of true legs prehensile. 



Genus. PHRONIMA. Head vertical ; tail ending in thread- 

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

 legs largest, and with pincers. Many seas. 



Genus. MKTCECUS. Two first pairs of legs shortest, and 

 with small pincers. Many seas. 



Order. L^MODIPODA. Abdomen very small, hardly 

 visible. Body cylindrical or depressed. Head very small. 



Family. CYAMID^E. Body depressed, oval. Eyes com- 

 pound. Antennae 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 

 together. 



Family. IDOTEID^E. 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. Antennas leg- 

 like. Northern Seas. 



Family. ASELLID^E. 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. Antennae 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. ONISCID^E. One pair of antenna;. 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. Omscus. Antennae eight-jointed, base hidden by 

 projecting front of head. Tail appendages four-jointed. 



Family. PoRCELLio. Antennae with seven joints. 



Family. ARMADILLIDiE. Oval, capable of rollling up 

 into a ball. Appendages of abdomen not beyond edge. 



Genus. ARMADILLO. Body convex and blunt. Outer an- 

 tennae seven-jointed. Last false feet with large basal joint. 



