THE ANNALS 



AND 



MAGAZINE OF NATURAL HISTORY. 



[THIRD SERIES.] 

 No. 104. AUGUST 1866. 



XIV. — Memoir on a new Parasitic Crustacean belonging to the 

 Order Lernseida, /or/nmy a new Family. By M. Hesse*. 



The object of this memoir is to make known a new Crustacean, 

 which, from the simplicity of its structure and the singularity 

 of its habits, must, I think, excite the curiosity of naturalists. 

 They will judge, from the description we shall give of it, of the 

 embarrassment in which we could not but find ourselves, in the 

 absence of all definite characters, to assign it a place in the 

 classification of organized creatures. 



§ 1 . Description. 



It is from 10 to 12 millimetres in length and 2 millims. in 

 breadth ; its body, covered with a parchment-like skin, is cylin- 

 drical and fusiform. It is essentially retractile in the direction 

 of its length ; and the segments of its abdomen, in consequence 

 of the width of their inferior margin, can even become invagi- 

 nated one within the other. It is divided mto five thoracic and 

 six abdominal segments. 



Seen from the back, the head terminates in a rounded point, 

 and presents in the middle a single eye, which, under different 

 degrees of incidence of light, exhibits a play of colours varying 

 from red to blue. 



The thoracic segments are not very distinct, with the exception 

 of the first two, which are easily recognized. The others are 

 merely indicated by lateral depressions, especially when this 

 part is tumefied by the accumulation of eggs ; they increase in 

 depth and width as they approach the base : the last, in parti- 

 cular, is much larger than the rest, is rounded laterally in the 

 middle, and then contracts at its junction with the first abdo- 

 minal segment. 



* Translated by W. S. Dallas, F.L.S., from the • Annales des Sciences 

 Naturelles,' serie 5. tome v. pp. 266-279. 



Ann. i^ Mag. N. Hist. Ser.3. Fo/.xviii. 6 



