M. Steenstrup on the genera Pachybdella and Peltogaster. 157 



more than a generic or subgeneric division, as the other half of 

 the original contents of the genus appears to be so closely allied 

 to this, and only to differ in the more elongated form of the 

 body, m the position of the sucking pit further from the extre- 

 mity, and almost under the middle of the body, and in the resi- 

 dence of the animal under the abdomen of a species belonging 

 to another family of Crustacea {Pagurus Bernhardus) . If there- 

 fore Pachybdella has proved to be a true Crustacean, analogy 

 leads us to regard Peltogaster in the same light. 



However, we need not perhaps rest entirely upon this conclu- 

 sion, as there are certainly direct observations in existence that 

 the young of the Pelfogaster-\ike sacs found under the abdomen 

 of the Macroura and Anomura (?) are Crustacean in form. Thus, 

 Diesing has not noticed that Kroyer, in his Monograph of the 

 Northern species of Hippolt/te, has briefly mentioned the para- 

 sites by which they are infested, and especially certain sac-like 

 creatures, which must undoubtedly be referred to the animals 

 now under consideration*. In the fourth section of the Mono- 

 graph, which bears the title of " Ein Paar Bemerkungen iiber 

 Schmarotzerthiere auf Hippolyten," the author, after describing 

 some other parasites, continues as follows (p. 56) : — " Lastly, 

 under the abdomen of Hippolt/te pusiola, I discovered an enig- 

 matical parasite (tab. 5. fig. 110 a) W'hich it is difficult to refer to 

 its right position, — nay, its structure appears so simple, so com- 

 pletely destitute of all organs, that one might perhaps easily be 

 led to regard it, not as an independent animal, but as a mere 

 pathological phfenomenon, a swelling or excrescence on the Hip- 

 poly tef. It evidently forms a new genus, which on the one 

 hand appears to have some analogy with the Lernseidse, and on 

 the other possesses an external affinity to some Hirudinete and 

 intestinal worms. Of this form I know several species : 1 found 

 one of a whitish colour and of considerable size, in abundance 

 on the abdomen of Pagurus puhescens near Spitzbergen ; another, 

 smaller and of an orange-red colour, occurred on Pagurus Bern- 

 hardus in the Kattegatt ; the third, which occurs on Hippolyte 

 pusiola, is nearly of a globular or oval form, of a white colour, 

 and about 2 lines in diameter. Of 25 specimens of //. pusiola, 

 eight bore these parasites under the abdomen ; some specimens 

 had two, and upon one I found no less than three of them. I 

 propose to describe these more fully on some other opportunity.^' 



* This is also noticed by Loven in his annual Reports. 



t " I should perhaps not have ventured to mention this creature decidedly 

 as a distinct animal, if I had not seen the eggs rush out on opening a spe- 

 cimen ; these, when examined under the microscope, exhibited fully deve- 

 loped young, consisting of an anterior body and an abdomen or tail, the 

 atter provided with swimming feet or bristles," &c. — Kroyer. 



