ART. 15 COPEPOD CRUSTACEANS OF CHESAPEAKE BAY WILSON 39 



Remarks. — Sars called this harpactid " a pronouncedly littoral 

 form, being only found in the uppermost part of the littoral zone, 

 and very often in shallow pools left by the tide." In Chesapeake 

 Bay it was almost wholly confined to winter and early spring. Be- 

 ing a new species established by Sars and afterward found by Steur, 

 Pesta, and Brian in the Mediterranean, it has never before been re- 

 ported from our American coast. Sars found only the female, but 

 Brian added the male of the species, and the present specimens in- 

 cluded also both sexes. 



ROBERTSONIA CHESAPEAKENSIS, new species 

 Pl^TEJ 4, A-I 



Specific characters of female. — Body fairly stout, almost cylindri- 

 cal; anterior portion considerably dilated, a little more than half 

 as wide as long, widest in the center. Cephalic segment nearly 

 equaling in length the entire thorax, widest across its posterior mar- 

 gin. Rostrum narrow-triangular, longer than wide and bluntly 

 pointed. Second, third, and fourth thoracic segments smoothly 

 rounded at their posterior corners. Posterior body three-quarters as 

 long and a little more than half as wide as the anterior. Genital 

 segment as long as the entire abdomen, with a transverse suture 

 near the center, which is distinct on the sides and ventral surface but 

 fades out on the dorsal surface. Abdomen of three segments, di- 

 minishing in length posteriorly ; anal segment with an angular notch 

 between the bases of the caudal rami; the latter wider than long, 

 obtusely truncated and tipped with two long and several shorter 

 setae. Eye small but fairly distinct. Egg case single. 



Specific characters of male. — Body regions similar to those of the 

 female, posterior body rather stouter; its segments fringed on their 

 posterior margins with slender spines, especially prominent on the 

 ventral surface. Terminal setae of caudal rami considerably stouter 

 than in the female, the longest one as long as the entire posterior 

 body. 



First antennae 7-segmented, rather densely setose, the fourth seg- 

 ment enlarged and armed with two aesthetasks. Second antennae 

 short and stout, the proximal segment a little longer than the distal 

 and armed on its anterior margin with a stout seta. The outer 

 ramus 2-segmented nearly as long as the distal segment and carrying 

 five setae, two lateral, and three terminal. Mandibular palp with 

 a broad, laminate terminal joint armed with a tuft of setae on its 

 rounded tip and a single longer one on the inner margin near the 

 center. Maxilliped of moderate size, the basal joint with two long 

 setae and several smaller ones at the anterior distal corner ; terminal 

 joint about as long as the basal and considerably swollen, with four 



