ENTOMOSTEACA OF MINNESOTA. 219 



0. gracilis not only has the disc like last foot colored bnt the swim- 

 ming antennse are banded with purple as in Slmocephalus rosfratns 

 Herrick and *S'. americanus Birge. The intestine has anterior caeca, 

 which is not the case in Lynceids, nor, indeed, in other Lgncodophnidw. 



The four-jointed ramus of the antennae approaches Lyvceidw in the 

 absence of a lateral seta, but the other ramus is as in Macroihrix. The 

 convolution of the intestine, the form of the post abdomen and the 

 situation of the anus are all of a stiictly lynceid type; moreover, the 

 flattened appendage of the last foot is like that of Euryeer ens. 



Even in the form of the shell there is a combination of characters; 

 the anterior part of the shell has the form peculiar to Lyncodaphnida'; 

 but posteriorly it again expands and becomes truncate behind; the 

 form in the adult is not unlike that of some Lynceidce, but the young 

 has a long spine posteriorly exactly like the spine of Baphnui. The 

 latter fact is very instructive, for it indicates that the theory proposed 

 (American Naturalist, 1882, p. 815) to explain the origin of this ap- 

 pendage is probably the correct one. Professor Leuckart suggested 

 that this spine was a balancing rod intended to keep the proper equi- 

 poise over the center of gravity; but it is difficult to see why these 

 long-bodied forms, in which the greater part of the weight lies 

 ''abaft" of the pivotal point — the base of the antencae — should be 

 thus provided while the shorter forms are not. We conceive that it 

 is an apparatus for effecting the moult of the inner lining of the brood 

 cavity of long-bodied and tender shelled animals such as Baphnia and 

 the present genus. The great development of the head in the crested 

 Baphnidw may undoubtedly be explained upon Professor Leuckart's 

 theory. 



*Ofryoxiis gracilis Sars. 



Plates XLII, Figs. 12-15; LVIII, Figs. 1-3; LIX, Fig. 2. 



Herrick '82 (Lyncodaphnia macrothroides). 



Sub-rectangular, greatly elongated, truncate behind, with a slight 

 spine above; head and eye small, fornix moderate, beak truncate; an- 

 tennules rather long, slightly curved, tapering a little toward the end, 

 whence spring three lanceolate spines and several sensory filaments, 

 five stout spines behind, above the middle, and several more slender 

 ones; swimming antennae very long, terminal setae smooth to the joint; 

 labrum as in Baphnia; mandible attached behind a salient angle of the 

 front margin of the shell; no abdominal processes; post-abdomen broad 

 above, triangular; terminal claws pectinate, furnished with one very 

 large toothed accessory spine and a smaller one; the first foot has a 

 hook; the last foot consists of a large oval plate which bears poste- 



