Prof. Allman on a new genus and species of Entomostraca. 7 



is manifest that it possesses very marked affinities with Cyclops, 

 while the dorsal situation of the receptacle for the ova presents 

 an analogy not to be overlooked with the other entomostracan 

 forms of Daphnia, Cypris and their allies. Its parasitical habits, 

 and the form of the appendages which immediately succeed to 

 the antennae, as well as its general conformation, would seem to 

 approximate it to Nordman's genus Ergasilius. From this suc- 

 torial parasite, however, the structure of its mouth will widely 

 separate it. Indeed it is perhaps hardly just to consider N. as- 

 cidicola as truly a parasite ; its habits in this respect would seem 

 to bear to those of other Entomostraca the same relation which 

 is found to subsist between the habits of Pinnotheres and those 

 of the generality of Decapods. 



The condition of the external receptacle for the ova I believe 

 to be one of the most remarkable peculiarities of the present 

 genus, and to be much more interesting than it may at first 

 sight appear. To this conclusion I have arrived from the con- 

 viction, that the organ in question is of a totally different nature 

 from the external egg-bearing pouches in Cyclops and its kin- 

 dred forms ; that while such pouches are only a portion of the 

 membrane of the true ovaries pushed outwards by the ova in the 

 act of extrusion, and finally allowing the escape of these by rup- 

 ture, the ovigerous receptacle in Notodelphys is the result of a 

 certain development of the superior arch of one or more of the 

 posterior thoracic rings expanded posteriorly and laterally so as 

 to form a kind of carapace destined for the protection of the 

 eggs. I believe it to be in every respect the representative of 

 the singular elytroid dorsal appendages to the thorax in Antho- 

 soma, Cecrops, and certain other suctorial Crustacea. In one of 

 the early stages of our Entomostracan, indeed, we may see at 

 each side the true ovarian pouches (the real representatives of 

 these appendages in Cyclops) projecting under cover of the 

 organ we are now considering ; the pouches then either continue 

 to increase by gradual protrusion till they fill the entire chamber 

 prepared for their reception, or else, becoming soon ruptured, 

 discharge their contained ova into the surrounding space, from 

 which, after having undergone there during a limited period a 

 certain incubatory action, these ova finally escape through the 

 definite opening already mentioned, without in any degree neces- 

 sitating the rupture of the walls of the ovigerous chamber, 

 such as must unavoidably occur in the closed pouches of Cy- 

 clops, &c. 



It is not easy to determine with certainty the exact elements 

 which enter into the composition of the ovigerous receptacle, 

 whether the whole of the dorsal arch is to be found in it or only 

 a part. From an examination however of what I look upon as the 

 corresponding organs in the suctorial Crustacea, I am of opinion 



