NO. 1504. AMERICAN PARASITIC COPEPODS— WILSON. 707 



which latter fills the whole of the anterior half of the nauplius. The 

 three pairs of appendages attached well forward and of the usual shape. 

 The first pair are not carried pointing directl}'^ forward side by side 

 as in the Caliginse, but extend outward at the sides of the body like 

 the other two pairs. The balancers are widely separated, elongate, 

 cylindrical throughout, very slender, and they taper to an acuminate 

 point. 



Total length 0.3 mm. Width 0.165 mm. 



This species is fairly abundant and the United States National Museum 

 collection includes ten lots, as follows: From the head of an unnamed 

 shark fourteen females and four males, taken at Clarion Island and 

 numbered 32724, U.S.N.M. (cotypes). From Mustdus cants three 

 females (Cat. No. 8122, U.S.N.M.); one female (Cat. No. 12665, 

 U.S.N.M.); one female (Cat. No. 32725, U.S.N.M.). From Carc/ia- 

 rias litto7xdis one female (Cat. No. 6205, U.S.N.M.); two females 

 and a male (Cat. No. 32726, U.S.N.M.). From Carcharias ohscvrm 

 three females (Cat. No. 6083, U.S.N.M.). From a pollack a single 

 female (Cat. No. 12664, U.S.N.M.). From a species of Trygon a sin- 

 gle female (Cat. No. 6210, U.S.N.M.). From a Bonito one female 

 (Cat. No. 32727, U.S.N.M.). 



In 1892 (as stated above, p. 702) van Beneden described "a new 

 genus" belonging to this subfamilj^ which he named Caligera^ with 

 the species difficiUs. His figures and descriptions plainly show that 

 the eopepod was really an Alehion^ and accordingly Bassett-Smith in 

 1899 changed the specific name which Beneden had given in order that 

 it might agree in gender with the name Alehkm. 



For he fell into the error of supposing that this name was neuter in 

 gender because it ended in "o^i," and hence he made the new name 

 ' ''Alehion difficile. " The present author made the same mistake without 

 looking up the derivation of the generic name. And the two new 

 species published in 1905 were named respectively ^'' gracile''' and 

 '''' glahrum.'^'' But Alehion is the name of one of Neptune's sons, hence 

 masculine in gender. 



Beneden's description is not very clear, but the points which he 

 emphasizes are sufficient to distinguish his species from the one here 

 described. In gracilis the free segment of the adult female is three- 

 fourths as wide as the genital segment, while its dorsal plates are 

 widely separated even at their bases. 



In difficills the free segment is onl}^ a little more than half the width 

 of the genital segment and its dorsal plates are close together with their 

 bases fused. But the greatest differences appear in the genital seg- 

 ment; in dfficil/s the body of this segment is longer than wide, while 

 the posterior processes are slender, cylindrical, and parallel. More- 

 over the entire dorsal and ventral surfaces as well as the margins are 

 covered with a thick coating of spines. But in gvactlis the bod}' of 



