"90 AliTKUAL REPORT. 



Of the two species liere described, one is certainly a member of this genus, 

 while the other is in many respects more like Dana's genus Hemicalanus, which 

 difiers from Diaptomus in not having the posterior feet of the female large and 

 stout and the shorter branch of the secondary antennae without the numerous 

 joints. The species of Hemicalanus are also oceanic, and none were seen to have 

 ova sacs. Both our species have single ova sacs, while one is not evidently 

 furnished with the plurality of articulations to second antennae. Not having 

 given a lull account of the family, it may be well to incorporate a more 

 general with the technical description. These animals are usually small, 

 seldom reaching one-fourth of an inch, but commonly appearing as mere 

 specks in the water. The body is canoe-shaped, and divided into two 

 portions. The main portion, or cephalothorax, is usually much the longest. 

 The antennae are the organs of iocomotion, being used as oars m the same man- 

 ner as the "water- boatman," etc., use the feet. The posterior pair of feet vary 

 with the sexes, as described above, the four following pairs are swimming organs, 

 while the anterior pair are modified and turned forward. 



The cephalothorax is more often. seven jointed in PontelUnce than in the Cal- 

 anince but this is not a constant character. 



Diaptomus longicornis, Herrick.* 



This speccies is very near to Z), castor and may^ indeed, be a variety of that 

 species, it differs, however, in shape and color from figures ot that species, and 

 the maxillae, and antennae differ considerably. Cephalothorax rather long, nar- 

 rowly oval, six-jointed; superior antennae, rather long but they are not curved 

 as represented in Dr. Baird's figures of D. castor. The male right antenna has 

 a geniculating joint at the thirteenth segment which is armed with a considerable 

 curved spine; the joints following are more or less enlarged and sometimes coa- 

 lesce, forming in extreme cases a monstrosity as represented in Geol. and Nat. 

 Hist. Rep. for 1876. The secondary antennae are two branched; the outer lamus 

 being three-jointed and armed at the extremity with three curved spines, form- 

 ing a sort of hand, the middle segment also bears a number of setae on the inner 

 margin, the minor ramus is six or seven -jointed, though it appears three-jointed 

 at first, the middle segment being sub-divided. The head is produced into a 

 beak in front but it is much smaller than in the following. 



The maxillepedes (or first pair of feet) are of three portions, the latter two 

 bearing setae which are directed towards the head, the final division is composed 

 of about six small joints each bearing a tuft of the sete. The remaining pairs 

 of feet are alike, each having two setigiferous rami. In the female the fifth pair 

 of feet are prehensile and stout, those of the male are unlike, the right being 

 long and the other rudimentary. 



This species is very brilliantly colored, the tips of the antennae and last seg- 

 ments of the abdomen are a fine bluish purple, while the body is variegated with 

 red, yellow and purple. The mass of eggs is also a beautiful red. Only one 

 locality is known to contain the creature, though it may be abundant in the more 

 marshy pools. In the Rep. of the Geol. Surv. of Minn, for 1878 it was men- 

 tioned and a figure given, but erroneously called cy clops. (See plate I.) 



*See D. sanguineus, Forbei in III. State Mus. Rep. 1876. Tlie description differs, ap- 

 parently, in several respects, notably as to color, but the species is cenainly closely 

 allied. 



