NO. 1788. NORTH AMERICAN ERGASILID^— WILSON. 305 



Leach's Anthosoma, Hermann's Dichelestium, and Risso's Nemesis. 

 Naturally the family diagnosis which he gave was made broad enough 

 to include all these genera, and was not of much value for Ergasilus 

 and Bomoloclius . 



Seven years later Milne Edwards in his great work on the Crustacea 

 retained this family but changed its name to ''Pachycephala, " and 

 subdivided it into two tribes or subfamilies, the Dichelestiens and the 

 Ergasiliens, including in the latter but three genera, Ergasilus, Bomo- 

 lochus, and Nicothoe. 



This was a manifest improvement, and his grouping forms the 

 basis of that accepted at the present time, the difference being that 

 his subfamilies or tribes have become separate families. 



In 1859 the Swedish naturalist, Thorell, published an excellent 

 paper on the copepods, which live in Ascidians. 



While these did not properly include any species belonging to the 

 Ergasilidse, yet Thorell's contribution is of special interest for two 

 reasons. He introduces a general systematization of the copepods, 

 both free-swimming and parasitic, dividing them into three groups. 

 The first of these he called the Gnathostoma, and described them as 

 having a pair of free mandibles and three pairs of maxillse without 

 any siphon. The second group were the Pcecilostoma, in which 

 there were no mandibles or siphon, while the number of maxillae 

 varied from three pairs to none. The third group were the Siphon- 

 ostoma, whose mouth was produced into a siphon inclosing the man- 

 dibles. He placed the Ergasilidse in the second group with many of 

 the new Ascidian semiparasites, which was equivalent, of course, to 

 declaring that in this family both mandibles and siphon were lack- 

 ing. To confirm this, in describing his new genus Lichomolgus, a near 

 relative of the Ergasilidse, he introduced figures of Ergasilus sieboldii 

 on plates 11 and 12 and tried to show that in this species there are no 

 mandibles. 



On this point, however, he was evidently mistaken, as has been 

 clearly shown by many subsequent writers, notably Claus (1864). 



Kroyer in 1863 added four new species of Bomolochus and four of 

 Ergasilus, and he professed to include both sexes of two species of the 

 latter genus. 



He made no attempt at a general classification, and so the value of 

 his contribution would lie chiefly in the discovery of the males of 

 Ergasilus and in a broadening of our knowledge of the two genera by 

 descriptions and figures of new species were it not for some serious 

 blunders. 



The species which he named Ergasilus gasterostei, one of the two for 

 which he gave both sexes, had been described by Pagenstecher in 

 1861 as TTiersites gasterostei. Kroyer had not seen this description, 



Proc. N. M. vol. 39— 10 22 



