1893.] NATURAL SCIENCES <>F PHILADELPHIA. 425 



Cocoons of this species are almost spherical and are borne on short 

 stout stalks. Usually they are attached to the broad surfaces of the 

 body, i. e., the sides of the carapace, inner faces of the anterior 

 abdominal epimera, and the sternal face of the tail fin. 



Length of cocoon without stalk *46 mm. 



The adults are found attached almost anywhere on the exterior of 

 the crayfish but more especially on the tergal surface. 

 Watauga Co. North Carolina, on Cambarus bartonii. 



B. instabilia, sp. nov. 



Fig. 3a, Plate XII, an unusually large individual seen from the 

 yentral side, showing the outlines of body and alimentary canal. 

 Drawn from a living individual in nearly full extension, x25. 



Fig. 36, and 3c, two views of the jaws, x200. 



Fig. 3e, a cocoon, x45. 



The constant movements of the lips, and the varying form of the 

 head and segments succeeding it during the life of the animal make 

 the name instabilia, the changeable, most appropriate. 



Body in a state of contraction very short and stout, the posterior 

 four segments forming a flattened disk- shaped expansion which is 

 scarcely longer than broad ; the first four body segments are much 

 more narrow, but increase somewhat in breadth to the fourth, pos- 

 terior to which the increase is very rapid to the seventh ; the eighth 

 is slightly narrower and develops lateral wing- like flaps, which, 

 sloping ventralward, bound a decided ventral concavity in this 

 region ; posteriorly they embrace the sucker-bearing segments. The 

 head and anterior segments are terete. Under normal conditions the 

 large head is considerably broader than the following segments, 

 which form a neck- like constriction, to which the head is attached by 

 a very mobile fold, forming a distinct annul us. The emarginated 

 lips are slightly creuulated, and form an almost continuous muscular 

 thickening around the mouth. The post-oral constriction is well 

 marked, but not so deep as in B. pulch&rrima. Numerous short 

 stiff hairs fringe the lips and head, and in young individuals are 

 present on the body segments also. 



The dark brown jaws are provided with four strong, curved, 

 conical teeth, which diverge slightly ; the outer pair are symmetrical, 

 the left tooth of the middle pair is much larger than the right ; this 

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