HISTORY OF THE AMERICAN MENHADEN. 281 



and then to divert himself with fishing, that, in forty years' observation, 

 he had never seen a bay-alewife without the louse. The shad begin to 

 return from the fresh water Jean and shotten about the end of May and 

 beginning of Juno, and continue descending during the remaining sum- 

 mer months. No one attempts then to catch them, for they are unfit for 

 the table. Whether the bay-alewife returns with the shad, I could not 

 learn, but it is certain that after June it is not thought worth the trouble 

 to catch them. No one could tell me positively whether the Oniscus still 

 continues with them, but it was the opinion of my informant, that, like 

 every other parasite, he deserts his protector in his reduced state, for he 

 could not recollect that he had ever seen him in the mouth of those 

 accidentally caught in the seine in July or August. 



I consider, therefore, the natural history of the Oniscus which I now 

 communicate as very imperfect ; and it were to be wished that some 

 lover of natural science would follow up the inquiry, by endeavoring to 

 ascertain whether he continue with, or quit the fish before his return 

 to the ocean, and also whether he be the Oniscus physodes of LinnaBus, 

 qui habitat in pelago. 



Should he be an insect hitherto undescribed, I think he might be very 

 aptly named, Oniscus prccgustator. 



The bay-alewife is not accurately described in any ichthyological 

 work which I have seen ; nor can I from my drawings, which were made 

 with a very weak hand, venture a description. From his having a reg- 

 ular prsegustator, I would suggest that he ought to be named Clupea 

 tyrannus. 



The Oniscus resembles the minion of a tyrant in other respects, for he 

 is not without those who suck him. Many of those which I caught had 

 two or three leeches on their bodies, adhering so closely that their 

 removal cost them their heads. Most of the marine Onisci appear to be 

 troublesome to some one or other fish. The Oniscus ceti is well known 

 as the plague of whales, and many of the rest are mentioned in Linnaeus 

 and Gmelin as pestes piscium. 



BENJA. HENRY LATROBE, F. A. P. S. 



P. S. — A gentleman well skilled in entomology informs me that he 

 believes that in Block's History of Fishes, a work not to be had in 

 Philadelphia, this Oniscus is mentioned. But, from a late examination 

 of Gmelin and Fabricius, I am convinced that the Oniscus prccgustator 

 is a species not hitherto accurately described. Gmelin had probably 

 seen the Linnaean insect, having changed the antennae utrinque duo 

 to antennis quaternis, and left out most of the long description given by 

 Linnaeus. Neither he, Linnaeus, nor Fabricius mentions the circum- 

 stance of habitation in the mouth of the fish, and the industrious and 

 copious Fabricius, who having changed the names of the genera, calls 

 him Cymothoa physodes, copies the description of Gmelin, excepting the 

 mention of the 4 antennae, which in his arrangement form a character 

 of the genus. 



