434 ' LIST OF FOSSILS. 



S. Bi'MisTiFORMis. Eishis. 



Animal subovatc, oblong, vrry smooth, nol serrated. Color olivaceous green ; under side, legs, and segmentary mar- 

 gins, ])ale ochraccous. Head a transverse square, inserted in a notch of the first abdominal segment. Eyes lateral, 

 reniforni, closely apiwoximating to the anterior portion of the first segment. Superior antenna slightly longer than the 

 head, three-jointed; the basal joint .subangular, much enlarged, and solid; terminating filament composed of numerous 

 small and short articulations. Inferior antenna; nearly double the length of the upper, four-jointed, and ending with 

 numerous short and smaller joints. Abdomen articulated into seven subequal segments, each containing beneath a pair 

 of perfect legs. Legs rather stout, each terminated by a strong slightly incurved nail. The segmentary impressed lines 

 on the basal segment of the tail do not extend to its lateral edges ; the terminating segment is triangular, and entire. 

 The s^vimming fins are much depressed ; the superior. one extends nearly the length of the segment ; the lower one is 

 about two-tliirds its length, and closes in under the superior- one shnilar to the sticks of a fan. The subcaudal branchial 

 lamina arc bifid ; one portion articulating on the other, not unlike the palpi on the jaw appendages. These laminse are 

 eight in number. 



In consequence of the near resemblance of tliis animal to the fossil genus Bumastus, it has received its specific appella- 

 tion. ^Vhen in a state of contraction, it assumes the form of a ball. 



Found in considerable abundance in pools left by the receding tides, along the shores of Cape Horn and its adjacent 

 islands. 



