ECONOMIC RELATIONS, ANATOMY, AND LIFE HISTORY OF GENUS LERN^A. 167 



anterior. Again, in 1867," he published a description of LertuBocera esocina, in which 

 he mentioned both gobina and gasierostei as distinct species, and added many details 

 of external and internal structure. In 1 863 Krc^yer added three new species, catoslomi, 

 pomotidis, and phoxinacea, to the genus, the first two of which were from the Mississippi 

 River. In 1865 Heller added another species, iagenula, obtained during the voyage of 

 the Novara. 



In 1870' Hartmann published the description of a species which he named barnimii, 

 together with excellent figures which included the eggs and the development up to the 

 raetanauplius stage. This is by far the best paper upon any species of the genus, and 

 it included as much of the internal structure as could be made out without sectioning. 



Meanwhile here in the United States Le Sueur had established in 1824" the first 

 American species, cruciata, upon material obtained in Lake Erie. After a long interval 

 he was followed by Kellicott with two other American species, one, tortua, from New 

 York State in 1881,"* and the other, pectoralis, from Michigan in 1882.' 



With these 10 species the genus remained until 1914,^ when Cunnington published 

 a short paper including a "List of described species" and three from the Tanganyika 

 region in Africa that were new to science. 



In spite of its brevity and omissions this paper proved to be of considerable value 

 because it summed up aM the described species and presented a key for their iden- 

 tification. Among other things, with reference to the genus, Cunnington stated, "A 

 careful study of these forms has given me the impression that two or three of them 

 may merit separation as distinct genera" (p. 822), but he wisely concluded not to do 

 this at present. On the next page he said: "The appendages appear to show compara- 

 tively minor differences within the limits of this genus, and have not been appealed to 

 for the purpose of establishing new species." 



The appendages certainly are remarkably similar in all the species examined by 

 the author, but this very fact precludes the establishment of new genera, for which 

 there must be characteristic differences in the appendages as well as in body form. 



Cunnington mentioned Kr^yer's catoslomi and pomotidis, Heller's Iagenula, and his 

 own diceracephala as possible candidates for the prospective new genera. 



The first three are shown to be good Lemseans in this paper. With reference to 

 Cunnington's species the chief distinctive feature mentioned is "the existence of only 

 two cephalic horns — apparently the dorsal pair — instead of four." But it may be noted 

 that the ventral pair in another of his species, temnocephala, are hardly large enough to 

 be called horns rather than spines, the ventral pair in variabilis and tenuis are also often 

 very minute, and in anomala they have entirely disappeared. 



These species certainly belong to the present genus in spite of considerable variation 

 in the number and structure of the horns, and the same is probably true of diceracephala. 

 Unless in addition to the lack of ventral horns or the presence of a dorsal horn there 

 were also well-marked differences in the appendages, it would be manifestly inadvisable 

 to establish any new genus. 



ECOLOGY. 



The parasites belonging to this genus are immovably anchored in the tissues of the 

 host's body. Consequently we should expect to find, as in the Lernseopodidae, consid- 



a Sit2ungsb. Gesellsch. Beford. ges. Naturw. Marburg, p. 5-12. d Proc. Amer. Soc. Micros., vol. a, p. 41. 



6 Arch. Anat. Physiol., p. 726-752. e Loc. cit., vol. 4, p. 75. 



t Jour. Acad. Nat. Sci. Phila., vol. 3, p. 286. / Proc. Zool. Soc. London, 1914, p. 819-829. 



