34 PROCEEDINGS OF THE ACADEMY OF • [Jail.^ 



Subgenus MARCOCYCLOPS Claus. 



Cyclops albidus Jurine. PI. I. 



Monoculus quadricorni^ var. albidus Jurine, '20, p. 44, pi. II, figs. 10 and 11. 

 Cyclops signatus var. tenuicornis Herrick and Turner, '95, pp. 106, 106, 



pi. XV, figs. 5-7; pi. XX, figs. 1-7; pi. XXXIII, figs. 1, 2. 

 Cyclops albidus Schmeil, '92, pp. 128-132, pi. I, figs. 8-146; pi. IV, fig. 15. 

 Ctjclops albidus Forbes, '97, pp. 47-49, pi. XIII. 

 Cyclops albidus Lilljeborg, '01, pp. 49-51, pi. Ill, figs. 21 and 22. 

 Cyclops albidus v. Daday, '06, p. 184. 

 Cyclops signatus annulicornis Byrnes, '09, pp. 10-13, pi. IV. 



Specific Description. — The first segment of the strongly arched 

 elliptical cephalothorax (PI. I, fig. 2), is in the proportion of 3 -.4 

 compared with the entire length of the cephalothorax. The lateral 

 angles of the segments are not prominent. The fifth segment is 

 rarely visible from above, owing to the arched form of the cephalo- 

 thorax. The first three segments are smooth along their posterior 

 borders. I find in all of the specimens examined from this locality 

 that the fourth segment has on its posterior border, laterally and 

 not extending to the median line, a row of very minute chitinous 

 serrations. These are only visible when the animal is turned on its 

 side. I find no mention of these serrations in any of the descriptions 

 of this species to which I have access. The fifth segment bears, 

 dorsally situated, three transverse rows of spinules. The last of 

 these is the only complete one and borders the segment posteriorly. 

 The second row does not extend to the median line. The first row 

 is quite short, lateral in position, and the spinules are considerably 

 larger than in the other two. Schmeil states in his note number 

 three, p. 130, that, with two exceptions, these rows of si^inules have 

 "never been observed." In Cragin's paper of '83 in his description 

 of Cyclops tenuicornis Claus (= Cyclops albidus Jurine), he saysi 

 "Either side of the fifth thoracic segment is furnished with three 

 transverse rows of serrulations, of which the posterior one is mar- 

 ginal. " Furthermore, he illustrates the point in his PI. II, fig. 13. 

 His drawing is inconsistent, however, with his description, as it does 

 not show the marginal row extending the entire width of the segment. 

 Forbes, very properly, does not mention the row of blimt spinules 

 between the insertion points of the fifth feet. This is not a "char- 

 acteristic, " as it is found in Cyclops fuscus Jurine. 



The width of the cephalothorax is to its length as 1 : 2. Its 

 length to that of the abdomen is as 7 : 4. (Schmeil reverses these 

 figures and gives abd. : ceph. : : 9 : 5, obviously an oversight). 



The abdomen is heavy; the first segment tapers only slightly, 

 but the enlargement at the anterior end extends beyond th(> width 



