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



the abdomen ; it is slightly lobed posteriorly, and filled with ova 

 of a deep olive-green colour, and in the angle between it and the 

 upper surface of the abdomen is an aperture through which the 

 ova escape at maturity (fig. 11) . As will hereafter be seen, it must 

 be viewed as formed by the confluence along the mesial line of 

 two pieces originally distinct. The large size of this organ and 

 the deep colour of the contained ova render it one of the most 

 striking features in the physiognomy of the little animal, and the 

 contrast which it presents with the surrounding lighter tissues 

 of the Ascidian makes the detection of the parasite a matter of 

 no difficulty. 



In company with N. ascidicola and differing in several import- 

 ant particulars from the latter as just described, I have not un- 

 frequently met with two little Crustaceans which deserve here 

 some attention. My belief is that they are not specifically di- 

 stinct from the subject of the present notice, but must rather be 

 viewed as immature states of this animal. In one of them (fig. 12) 

 the antenna? (fig. 13) are geniculated, and consist of a thick pe- 

 duncle, from which the terminal portion, which is subulate, mul- 

 tiarticulate and setigerous, passes off abruptly at an angle. The 

 cephalic segment carries no proper feet, and the thorax presents 

 three distinct rings with a pair of natatory feet attached to each ; 

 the fourth pair is borne as in the adult, beneath the anterior ex- 

 tremity of the ovigerous sac, and at a short distance behind these 

 last is a pair of small stiliform organs terminated by setae. The 

 last ring of the abdomen is bilobed, and is prolonged by a pair 

 of cylindrical appendages. The ovigerous sac is disproportionately 

 large, and the habits of the animal are peculiarly sluggish. 



The other (figs. 14 and 15) differs still more from the adult 

 than does that just described. The antennae are short and thick, 

 and not geniculated. The cephalic segment, as in the last, sup- 

 ports no locomotive feet, while four distinct rings may be demon- 

 strated in the thorax, each bearing a pair of biramous natatory 

 feet, and the abdomen would appear to be composed of five seg- 

 ments, the last terminated as usual by a pair of cylindrical ap- 

 pendages. The external receptacle for the ova presents itself in 

 this little animal as two hollow organs perfectly distinct from one 

 another except at their origin. They appear to arise immediately 

 behind the fourth thoracic ring, and are thence continued back- 

 wards, embracing the sides of the abdomen. 



The mouth is provided with a very large labrum (fig. 16), which 

 is prolonged anteriorly by means of a conical projection between 

 the bases of the antennae. The labrum conceals two strong den- 

 ticulated mandibles (fig. 17), and the oral apparatus is completed 

 by two pairs of maxillae and three additional pairs of appendages 

 (figs. 18 — 20) as in the adult; of these last, that which im- 



