48 PROCEEDINGS OP THE ACADEMY OP 



abdominal segment; thence tapering, at first rapidly, and then very gradu- 

 ally, to a mucronate point, upper and lower margins setigerous, like those of 

 the stylets. 



It is possible that when we can have an opportunity to examine additional 

 specimens, we may have to modify some of the characters given in the fore- 

 going generic or specific description ; though not, we believe, in any very 

 essential particular. We hope, however, to be able, hereafter, to clear up 

 several doubtful points in the structure of this interesting type, when we can 

 have better specimens for study. 



Length from anterior side of head to the extremity of the penultimate ab- 

 dominal segment 1.30 inches ; length of telson 0-31 inch ; length of the first 

 six abdominal segments 0*52 inch ; length of the seven thoracic segments 

 about 0-64 inch. Height of third abdominal segment 0-20 ; height of each 

 first two or three thoracic segments 0-12 inch ; length of stylets about 0-31 

 inch, of which the first joint forms only about 0-06 inch. Length of outer 

 antennae, including its peduncle, 0-66 inch. 



It is with pleasure that we dedicate this typical species of a new and 

 remarkable extinct genus to our friend Dr. William Stimpson, whose labors 

 in carcinology, and various other departments of zoology, are well known 

 iu this country and Europe. 



ACANTHOTELSON IN^EQUALIS, M. & W. 



The specimen upon which we propose to found this species, appears to 

 agree with the last in almost every respect, excepting in the proportional 

 size and the form of the segments. In the first place, the penultimate ab- 

 dominal segment is nearly twice the length of any of the others, instead of 

 being nearly or quite of the same length ; while the other abdominal seg- 

 ments (as seen in a side view) are more cuneiform than in the last. Again, 

 the fifth and sixth thoracic segments are longer, particularly above, and the 

 fourth shorter, than any of the others, instead of all being of about the same 

 length. We have not been able to see the stylets, nor to make out the nature 

 of the legs, but from a part of one of those of the anterior pair, they would 

 seem to be rather stouter than in the last described species. 



As these differences can scarcely be due to accidental distortion, we can 

 but regard this form, with the material now at hand for comparison, as a 

 distinct species. If we are correct in this view, it is probable good examples 

 will show other differences than those mentioned above. 



Length of head, thorax and abdomen 0-90 inch ; length of head 0-12 inch ; 

 length of the seven thoracic segments about 0-50 ; length of first five ab- 

 dominal segments 0-26 inch ; length of penultimate abdominal segment 0-09. 

 Height of third abdominal segment (flattened side view) 0-13 inch ; height of 

 anterior thoracic segments about 07 inch. Length of lower antennae at least 

 0-43 inch ; length of upper not less than 0-36 inch, and probably a little 

 more. 



? Family PAL.EOCARIDJE. 



Genus PALJ30CARIS, Meek k Worthen. 



Inner and outer pairs of antennas of nearly equal length, the former each 

 bearing a well developed accessory appendage ; peduncles of both pairs 

 shorter than the flagella. Head about as long as the first two abdominal 

 segments. Thoracic legs long and slender ; anterior pair not chelate. Tel- 

 son long, tapering and horizontally flattened ; stylets with first joint very 

 small, second double, and also flattened horizontally. 



This is another remarkable type, presenting, so far as can be determined, 

 even a more puzzling combination of characters than that we have described 

 under the name Ac.anthotelson. In the nature of its antennae, with their ap- 

 parently well-developed basal scales, the structure of its caudal appendages, 

 and its lono-, slender legs, spread out on each side, for walking in an erect 



[Mar. 



