312 GEOLOGICAL SURVEY OF THE TEEEITORIES. 



under side are miicli shorter and stouter than in E. texana; the stem 

 is shorter and stouter than that of JE. texana. 



Eighteen pairs of feet. 



Telsou rather broad ; along the dorsal edge are twelve pairs of acute 

 spiuules with the usual long forked filament between the first and second 

 pair of spines; the large terminal spines of the telson fringed with long 

 hair-like set* instead of spines, as in the European Limnadia ffigas, but 

 the tip is armed with minute short spines, A stout conspicuous spine on 

 the lower angle of the telson under the terminal spines. A pair of long 

 abdominal cirri. The eggs are yellowish and roughly granulated. 



Length of shell, G.2°^°^ ; breadth, 3.8"^'". 



About one hundred females, mostly with eggs, occurred in a small 

 pool of fresh water on Penikese Island, Buzzard's Bay, August 27, 1873, 

 collected by Mr. Walter Faxon. Upon examining the pool the following 

 July or August (1874), the young, about a line in length were found, 

 but the pond subsequently dried ui). The eggs are yellowish and with 

 the chorion roughly granulated. 



The species was dedicated to Prof. L. Agassiz. 



Compared with L. americana Morse, which closely resembles L. gigas 

 (received from Sweden through the kindness of Prof. W. Lilljeborg), it 

 d lifers very decidedly in the much narrower shell and fewer lines of 

 growth. It belongs to a different genus from the two above-named spe- 

 cies, agreeing in the structure of the animal and the bivalved carapace 

 with L. antillarum Baird, Proc. Zool. Soc, 1852, 30, from St. Domingo 

 (Fig. 15), and L. texana Pack. From L. antillarmn it differs in being 

 more regularly oval and much more prominent behind the umbones. 

 It also agrees with Baird's description of L. antillarum in its two large 

 terminal caudal spines being hairy, it having eighteen feet and nine- 

 jointed flagella. It differs from L. texana in the stouter haft-organ, be- 

 ing less triangular in outline; in the broader telson, on the upper edge 

 of which the teeth are less numerous ; in the smaller first antennae, and 

 the less spiny second pair; the shell differs in being more broadly ovate 

 than in U. texana, which is oblong, less concave along the dorsal edge, 

 and it differs from that of E. texana in having four instead of five lines 

 of growth, as in L. texana. 



EuLiMNADiA TEXANA Packard. 



Plates VI, VII, figs. 1-4. 

 EuUmnadia texana Packard, Amer. Jour. Sc, vol. ii, Aug. 1871. 



Carapace valves rounded, oval, whitish, with 5 concentric lines of 

 growth ; shell very minutely punctured ; these markings being coarser at 

 the posterior end of the shell, where they are arranged in lines parallel 

 to the edge of the shell ; eyes double, but with the inner edges contiguous. 

 Twenty body-segments behind the head, including the telson ; 18 pairs 

 of feet ; first antennae extending to the first joint of the flagella of sec- 

 ond pair; the latter each 9-jointed, each joint above with 4 or 5 stout 

 setse, and beneath with long spinulose setse. First pair of legs of male 

 with a slender hand ; the claw moderately large, the fifth endite very 

 long and slender. 



Telson with sixteen fine teeth above, not including the terminal acute 

 spine; ckudal appendages long and slender, knife-shaped, the under 

 edge fringed with long hairs; the upper edge straight, the end blunt, 

 with the lower edge slightly curved. The eggs are yellowish and pen- 

 tagonal in outline. 



Length of shell, 7°^°^ ; breadth, 4'"'". 



" Quite common in many places in Western Texas in the early spring" 



