270 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 117 



Color. — Distinctive pattern of blue pigment on ventral surface 

 of prosome : ± -shaped patch in center of head between and behind 

 ganglia; a spot at base of each A2 and a spot in midline between these 

 (female) or a little more posterior (male) ; a much brighter and more 

 conspicuous spot behind Bl of each Pi. 



This is the only species of Oithona in the Puerto Eican bays 

 investigated that has pigment in the prosome; hence, identification is 

 easy in freshly preserved collections. 



Remarks. — Oithona hehes was described briefly by Giesbrecht in 

 1889 from 2 females collected at the mouth of the Guayaquil River, 

 Ecuador. Grandori (1912) reported 3 females from Laguna Veneta, 

 Italy, but his identification was not supported by any description or 

 illustration and must be considered questionable. Although listed 

 in generic revisions, the species was not discovered again until Kiefer 

 (1936) received several females and 2 males from Maria Farinha, in 

 northeast Brazil, and redescribed it. The Puerto Rican specimens 

 fit closely the accounts of 0. hehes given by Giesbrecht and by Kiefer 

 except that the caudal rami are relatively longer. In the specimens 

 from Ecuador and from Brazil the rami are only about twice as long 

 as wide, while in the Puerto Rican specimens the rami are 3 times as 

 long as wide. A number of specimens from Puerto Rico were sent 

 to Dr. Kiefer at Konstanz ; he kindly compared them with his Brazilian 

 specimens and reported good agreement except in the length : width 

 ratio of the caudal rami. Dr. Kiefer also pointed out a character 

 that we had overlooked: the robust distal inner seta of Ri2 of P4. 



In the genus Oithona, considerable significance is given to the 

 relative lengths of the caudal setae. Unfortunately, Giesbrecht gives 

 no information on these setae in his accounts of 0. hehes, and the 

 lateral apical setae were broken in Kiefer's specimens. After receiving 

 Puerto Rican specimens from us. Dr. Kiefer reexamined his Brazilian 

 material and confirmed his earlier report on the incompleteness of 

 the caudal setae, but he also wrote: "Nachdem diesen Befunden muss 

 ich aber annehmen, das die ausserste Endborste auch bei den brasil- 

 ianischen Tieren mindestens halb so lang wie die innerste war" (in 

 litt., March 2, 1963). 



In his key to the species of Oithona, the late K. Lindberg (1950) 

 separates 0. dissimilis and 0. hehes by the relative lengths of their 

 medial and lateral apical caudal setae. Lindberg indicates that the 

 medial apical seta is about 4 times as long as the lateral apical seta in 

 0. hehes but not more than 2.5 times as long in 0. dissimilis. (In 

 his original description of 0. dissimilis (1940), the ratio is 2.2-2.3). 

 Thus, in Lindberg's key the Puerto Rican specimens run to 0. dis- 

 similis; however, in 0. dissimilis, from brackish water on the east 

 coast of India, the head is truncate rather than pointed anteriorly; 



