298 GEOLOGICAL SURVEY OF THE TERRITORIES. 



male koepiug the eggs in place. 1st (Limnetis), or usually the 1st and 

 2d, pair of feet in the male provided with a, hand ; the 4th, 5th, and Gtli 

 endites modified to form a claw, finger, and thumb-like clasping organs. 

 Posterior segments each bearing a pair of spines; the telsou large, com- 

 pressed, often spined, and bearing a pair of caudal appendages. Larvse 

 nauplius-shaped. 



Subfamily LIMNETIN^ Packard. 



Shell nearly spherical, with no lines of growth ; rostrum very large and 

 broad at the end, mucronate in the females, broad and truncate in the 

 males; 10-12 pairs of feet ; in the males only the 1st pair provided with 

 a hand; terminal segments of the body not spined; telson undeveloped. 



But a single genus, Limnetis. 



Genus LIMNETIS Loven. 



Limnetis Lov^n, Kongl. Vet. Akad. Ilaudlingar, Tab. IV, 203, 1845; 



Ofversigt Vet. Akad. Forhandl. 57, 184G; Wiegmann's Archiv, II, 203, 



1847. 

 Hedessa Lievin, Neueste Schrift. der naturf. Gesellsch. in Danzig, IV, 



Heft II, 4. Tab., I, II. 

 Hedessa Siebold, Neueste Preuss. Provincialbl. VII (XLI), Heft 3, 198, 



1849. 



Carapace bivalved, nearly spherical, oval, smooth ; polished fine punc- 

 ture-like marks in the i^arenchyma of the shell, giving it the appearance 

 of being finely punctured ; no beaks or umbones. Head large, the fiont 

 bearing the eyes enormous, and produced into a very large rostrum, 

 either truncated in 9 and either mucronated or truncated in <? in front. 

 Eyes small, sometimes separate. First antennsB minute, slightly el- 

 bowed, with indications of three joints; second antennae with scape or 

 base rather short ; the flagella rather short, composed of from 15 to 21 

 joints, with remarkably long setaj. From ^1 to 12 pairs of feet; in the 

 males the anterior pair converted into a complicated hand ; the end of 

 the abdomen blunt, simple, with no spines. 



The species of this genus are readily recognized by the spherical 

 small, smooth shell, with no lines of growth, entirely inclosing the 

 animal; by the enormous head, the large broad rostrum; the few feet, 

 there being but one pair of hands in the males, instead of two, as in 

 Ustheria, and by the simple unarmed telson. The antennse are shorter 

 and thicker than in Estheria. They are sometimes mistaken by shell 

 collectors for specimens of Cyclas or Pisidium. They swim on their 

 backs, with the shell a little open, in a graceful but not very rapid man- 

 ner compared with the Ostracoda. 



Synopsis of the species. 



Shell subsiDherical, small, front of head of male narrow; 



second antennae 16-jointed ; flabellum very large L. gouldii. 



Shell large, suboval; front of male broad and square; 

 second antennae 14 and 17-jointed; flabellum remark- 

 ably narrow L. mucronatus. 



Shell large, suboval ; front broader than in any other spe- 

 cies except ^raciZicornis' ; antennae 20-join ted; gill very 

 large, flabellum shoi-t and broad L. hrevifrons. 



Shell small, subspherical ; front very broad; antennae long, 



20-jointed X. gracilicornis. 



