46 PEOCEEDINGS OF THE NATIONAL MUSEUM vol.80 



METACYCLOPS GRACIUS (LUIjeborg) 



Cyclops gracilis Lilljbbokg, De Crustaceis ex ordinibus tribus in Scania occur- 



rentibus, Appendix, p. 208, 1853. 

 Mesocyclops gracilis G. O. Saes, Crustacea of Norway, vol. 6, p. 63; pi. 39, 



1914. 

 Metacyclops gracilis Kiefeb, Das Tierreich, Lief. 53, p. 72, 1929. 



Occurrence. — Fourteen specimens of this species were taken in a 

 surface net at Station Z on October 17, 1920, in water 13 meters deep 

 over a muddy bottom. 



Remarks. — This is a fresh-water species that has been found in 

 central Europe and on the Scandinavian peninsula, but has not been 

 heretofore reported from American waters. The salinity at the 

 surface where the specimens were obtained was 10.4, which is not 

 high enough to offer any serious obstacle to their presence. They 

 might easily have drifted out of the Patapsco Kiver, the mouth of 

 which is just above Station Z. But it is also evident that their 

 presence at the station was accidental, and that they are not likely to 

 be found in any abundance or to be widely distributed in the bay. 



OITHONA BREVICOBNIS Giesbrecht 



Plate 3, I ; Plate 5, I-N 



Oithona hrcvicornis Giesbrecht, Atti Accademei Lincei, Rome, ser. 4, vol. 7, p. 

 475, 1891; Fauna und Flora des Golfes von Neapel, vol. 19, 538, pi. 34, 

 figs. 6, 7, 1892.— Farban, Proc. Zool. Soc. London, 1913, p. 191. 



Farran gave the following specific characters in the reference given 

 above : " Eostrum present, ventrally directed, short, curved, not visi- 

 ble in dorsal view ; exopod of first foot with 1.1.3 outer edge spines ; 

 exopod of fourth foot with 1.1.2 outer edge spines; length 0.7 mm." 

 Giesbrecht in the second reference above, under the diagnoses of the 

 species of Oithona on page 754, enumerated the following characters 

 for the present species : " Forehead ending in a pointed rostrum, 

 directed ventrally and not visible in dorsal view. First antennae 

 scarcely reaching the posterior margin of the front body or falling 

 distinctly short of it. Furca longer than the anal segment. Length 

 0.7 mm." The present specimens agree with these diagnoses except 

 that the caudal rami are sometimes apparently shorter than the anal 

 segment. In Giesbrecht's figure of the female in dorsal view (pi. 

 34, fig. 6) he put in a short anal segment next to the caudal rami 

 similar to the one seen in the male. This was visible in about half the 

 Chesapeake Bay specimens, but in the other half it was indistinguish- 

 ably fused with the segment in front of it, and the two together were 

 longer than the caudal rami. Giesbrecht also wrote that the male was 

 unknown, and Farran accepted his statement. The only description 

 of the female is the one given by Giesbrecht, which is extremely 

 brief and tells us nothing about the appendages. Accordingly a 



