114 THE ROTIFEEA. 



narrower. The foliations are so slight as to permit the lateral antennae with their 

 nerve-threads to be easily seen. Their rocket-shaped extremities lie close to the lorica, 

 not far from its edge, and between the first and second bosses on either side : they are 

 therefore, in an unusually forward position. The lateral canals can also be traced, 

 in many convolutions, from the lower part of the head, to the point where they are 

 abruptly cut off by the gastric glands. In young specimens, in which the ovary is a 

 small, transverse, pyriform sac, and so does not obscure the view, they are seen again 

 below the gastric glands on either side of the stomach ; and, passing behind it, appear to 

 end below it on either side, in small pear-shaped expansions. I could never find any 

 contractile vesicle ; but, under favourable conditions, I have seen three pairs of 

 vibratile tags : one a little above the heads of the gastric glands, one on a level with 

 the middle of the stomach, and one not far from the pear-shaped sacs in which the 

 lateral canals seem to end. 



Length. Lorica, ^ inch. Habitat. Abbot's Pond, Clifton (C.T.H.) : not common. 

 Abundant near Torquay (P.H.G.). 



I met once with an empty lorica (PI. XXVI. fig. 17) which I suppose to be that of 

 Ehrenberg's P. elliptica. It came from a pond in Button Park, Birmingham. 

 ' 



P. MUCRONATA, Gosse, sp. nov. 

 (PI. XXVI. fig. 15.) 



[SP. CH. Lorica usually circular; dorsal plate furnished with an acute mucro 

 projecting from its front. Lacustrine. 



In April 1885, associated with P. patina and P. valvata, which were swarming in 

 one of my window reservoirs, I first met with this very pretty form. It never became 

 very numerous ; but, in the course of a few weeks, during which I was paying special 

 attention to the genus, I met with more than thirty examples. The thought occurred 

 that it might be the young condition of one of its larger fellow-species ; and, if so, valvata 

 would be the more probable. Yet I have found the young of valvata no larger than 

 mucronata, but with no trace of the mucro : and I have seen a nearly mature egg in 

 mucronata, which, though not conclusive, augments the probability of adult condition. 

 On the other hand, slight unevenness of frontal outline is not rarely discernible in adult 

 specimens of both the larger species. The matter is still subjudice', but for the present 

 mucronata seems worthy of specific rank. 



The lorica has not only the intra-marginal granulation of its fellows, which gives 

 them so elegant a resemblance to a new silver coin, but is shagreened or studded with 

 close-set rugosities over the entire surface of the dorsal plate, so delicate, however, 

 that the hyaline transparency is not interrupted. What I consider the branchial organs 

 are small ; the efferent lobe, answering to the pyriform (gastric gland), is generally 

 inconspicuous, and the afferent tubes are clustered in form of a cone around the base of 

 the sub-horizontal muscle. I have not satisfactorily observed the existence of eyes. 

 The pair of diagonal muscles is unusually well-developed. The lorica has about two- 

 thirds of the diameter of valvata. P.H.G.] 



Length. About y^ inch. Habitat. A domestic aquarium (P.H.G.) : rare. 



P. CLYPEATA, Ehrenberg. 



(PI. XXVI. fig. 14.) 

 Ptcrodina clypcata . . . Ehrenberg, Die In/us. 1838, p. 518, Taf. Ixiv. fig. 6. 



[SP. CH. Lorica elliptical, truncate at each end ; coronal disks widely separated. 

 Marine. 



I first formed acquaintance with this attractive species in July 1850, in sea-water 

 from the Essex coast ; and lately it has been sent me in abundance by Mr. Hood from 



