NO. 1788. NORTH AMERICAN ERGASILID^— WILSON. 353 



This genus was established by Kroyer in 1837 with a short descrip- 

 tion and seven figures. He had but a single specimen, a female 

 taken from the inner surface of the pectoral fin of a Diodon hystrix in 

 the Danish West Indies. And his account includes only the external 

 characters with none of the appendages except one pair of attachment 

 organs. 



From its degenerate form and general shape he placed the parasite 

 in the family of DichelestiidaB. 



Twenty-seven years later (1864) Nordmann published a second 

 account, based upon ten specimens obtained from a Diodon species 

 on the west coast of Africa. He corrected and supplemented Kroyer's 

 description and gave a figure of the under surface of the cephalothorax 

 showing three pairs of appendages, which he named first and second 

 antennae and second maxillipeds. He claimed that the structures 

 which Kr63^er had described as attachment organs were only the 

 thickened border of the winglike processes on the sides of the cephalo- 

 thorax and that what he himself presented as second antennse were 

 the true attachment organs. But Nordmann did not discover any 

 of the other appendages, and simply shows the difi'erences in body shape 

 between his specimens and Kroyer's. He describes the epidermis 

 as covered on both the upper and under surfaces with small conical 

 warts (Warzen). He also saw what he suggested might be a proboscis 

 (Russel) and classifies the genus among the Chondracanthidge. 



Bassett-Smith in 1899 puts it back among the Dichelestiidas, fol- 

 lowing Kroyer. No other writer has done more than to mention 

 the species, and the genus is left where Kroyer and Bassett-Smith 

 placed it, in the Dichelestiidse. And this is where it would naturally 

 be placed by reason of its body form, but a single look at the true 

 mouth-parts is enough to show that it is a Bomolochid genus. 



Neither Kroyer nor Nordmann saw any of the mouth-parts except 

 the maxillipeds, which were the appendages Kroyer described as attach- 

 ment organs, and also those which Nordmann called second antennae, 

 the difference in structure being due to the fact that they were describ- 

 ing different species. 



The appendages which Nordmann called second maxillipeds were 

 probably the second pair of swimming legs, as will be seen in the 

 description hereafter given. The reason why both these investiga- 

 tors failed to fuid the mouth-parts is simple but effective. They lie, 

 as already stated, in the bottom of a bowl-shaped depression; when 

 taken from the fish's fin this depression is filled with slime, which 

 efl'ectually conceals the appendages. In preservatives this slime 

 becomes hardened and is then very difficult to remove. Both of 

 the investigators above mentioned were working with material that 

 had been in alcohol for a long time, and the only thing visible was the 

 maxillipeds, whose tips project above the rim of the depression. 

 Troc. N. M. vol. 39— 10 25 



