COMPENDIUM OF GENERIC DISTINCTIONS. 



Genus. ASTACUS. Beak wide at base, depressed; one 

 tooth on each side. Fresh running waters. 



Tribe. CARIDITA .Abdomen very large, horny. Outer 

 antennse with very large plate at base. Base of false feet 

 covered by projections of segments. 



Family. CEANGONID^!. Both pairs of antennae on 

 same line. First pair of legs with small pincers. 



Genus. CBANGON. Carapace flattened ; claw also flat- 

 tened. Second and third pairs of legs very slender ; fourth 

 find fifth strongest. Many seas. 



Family. ALPHEID5!. Antennae in two rows, nine above. 

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



Genus. ALPHEUS. 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 

 lilaments on inner antennas. First pair of legs large, power- 

 ful, and unequal ; pincers thick. Eyes not prominent, but 

 projecting beyond carapace. Many seas. 



Family. PAL33MONID.&!. Beak long, compressed, and 

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

 and fifth pairs one-toed. 



Genus. PANDALUS. Outer antennse 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. PALJEMON. Inner antennas with three filaments. 

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



Genus. HIPPOLYTE. Beak large and compressed. Inner 

 antennae tipped with two many-jointed filaments. Many 

 seas. 



Family. PMWBIDJB. Antauwe in two rows, lower or 

 both pairs long. Beak long and compressed ; abdomen also 

 long and compressed. 



Genus. PENJEUB. Tnner antennae short ; first joint of 

 ypper antennae 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 antennw 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 

 cylinders. Seven or eight pairs of legs, mostly near tho 

 mouth. 



Family MYSIDJE. Carapace with folded edges, thorax 

 thick and compressed at sides. Abdomen large ; sis to 

 eight pairs of legs on thorax, each with a large palpus, look- 

 teg much like another leg. 



I??M. MYSIS. Nogills on thorax. False feetof abduncn 

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

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



Family. PHYLLOSOMIDJE. Carapace flat, men.bni- 

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

 mostly slender. No scales at base of outer antemuu. 

 Abdomen small. One genus. Atlantic and Eastern seas. 



Family. EB,ICHTHID.ffi. Carapace membranous, trans- 

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

 Eyes thick and globular. 



Genus. EBICHTHUS. First joint of eye-footstalks shorter 

 than second. Hinder angles of carapace sharply pointed. 



Family. SQUILLIDJE. 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. SQUILLA.- 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. E D R I O P H T H A L_ M A T A .- Eyes 

 esssile ; body in three portions. Respiration through modi- 

 fied limbs. 



Ordnr 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 ana 

 used for locomotion. 



Family. ORCHESTID.3S. Formed for leaping ; l>ody 



compressed, no palpus on mandibles. Two short appendage* 

 to tail. Upper antennse shorter than basal joints of lower 

 antennae. 



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. GAMMARID^!. Formed for swimming, palpus 

 on mandibles. Antennas 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. SULCATOK. Upper antennas half length of lower, 

 forked, with second joint flattened. Second and third pairs 

 of legs two-clawed. Most seas. 



Genus. GAMMARUS. Upper antennse 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. COEOPHID^l. Formed for walking. Body 

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

 mandibles. Antennae-like logs. 



Genus. CERAPUS. No lush on antennse. 

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



Genus. COBOPHTOM. Lower antcnnso very large ami 

 without lash, first pair of legs with a lash. Body long, 

 cylindrical, rather compressed. Many seas. 



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

 domen united. Antennre short and leg-like. Six points on 



Genus. CHELDRA. Upper antenmc shorter than lower, 

 and with an appendage. Fourth to sixth segments f 

 together. Many seas. 



Tribe. IIVPJSRITA.lle&d very large ; mandibles also 

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

 jointed. Some legs prehensile ; end of abdomen for swimn: ing. 



Family. PHRONIMAD-ffi. Second pair of antenna: st 

 and bristle-like ; some of true legs prehensile. 



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

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

 U-Ljs largest, and with pincers. Many seas. 



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

 with small pincers. Many seas. 



Order. IJEMODIFODA. Abdomen very small, hardly 

 visible. Body cylindrical or depressed. Head very small. 



Family. CYAMID-ffi. Body depressed, oval. Kycs com- 

 pound. Antennso close at base. Five pairs of legs, all i>n- 

 hensile. Respiratory apparatus on second and third jo.nts 

 of thorax. 



Genuf. 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 legsverj 

 large and flat, covering all under side of abdomen, fam 

 segment very large and shield-like. 



Genui. ARCTURUS. Body long. Three last pairs of legs 

 used for walking ; four first pairs flat at tips. Anter 

 leg-like. Northern Seas. 



Family. ASELLID.E. Body long. First pair of antenna? 

 very small. Abdomen jointed, last joint large and shiel< 

 like ; tip of abdomen with pointed appendages. 



Genus. LntNOBlA. Body capable of being curled i 

 Eyes distinct. Antennas in pairs, one pair over the ( 

 Tail of many segments. Many seas. 



Genus. ASELLUS. Front legs largest. Body oblong, 

 flattened, nine-jointed ; one joint for the head, seven forth 

 thorax, and one for the abdomen. Tail appendages long. 

 Fresh waters. 



Famil!/. ONISCID^E One pair of antennse. Abdomen 

 of six segments, last rather small. Legs slender. _ 



Genus LIGIA.- Outer antennae with last joint com- 

 pound. Four appendages to tail, two on each side. 



Genus Oxrscus. Antcnnie eight-jointed, base hidd 

 bv projecting front of head. Tail appendages four-jointed. 

 " Family. I'ORCELI io. Antennse with seven joints 



