HYDATINAD^E. 



a tube, rich in Rotifera, sent me by Mr. Bolton in the autumn of 1884. It had become, 

 in the live-box, accidentally entangled in a small mass of tenacious mucus, which 

 evidently annoyed it, and from which it made vigorous but ineffectual efforts to become 

 free. I have never met with the form since. P.H.G.] 



Length of body (without styles), about T }- G inch. Habitat. A pool near Birmingham 

 (P.H.G.). 



Family IX. HYDATINAD^. 



Corona truncate ivith styligerous prominences ; ciliary wreath two parallel curves, 

 the one marginal fringing the corona and buccal orifice, and the other lying within the 

 first, the styligerous prominences being between the two ; trophi malleate ; foot furcate. 



Ehrenberg's very extensive family of the Hydatincea, under the name of Hydatinadce, 

 is here restricted to three genera, viz. Hydatina, Notops, and Rhinops. They are all 

 alike in their corona, ciliary wreaths, and trophi, but differ from each other in their 

 shape, eyes, and foot. 



The head is truncate with a deep cup-like cavity as it were scooped out of it. This 

 cavity lies more towards the ventral surface than the dorsal, so that a transverse slice 

 would be horseshoe-shaped, the bend of the horseshoe being to the dorsal surface. 

 The principal wreath fringes the outer edge of the cup's wall, and the secondary wreath 

 borders the inner ; both wreaths are continued down into the buccal orifice, which lies 

 just within a deep notch in the wall of the cup 011 the ventral surface. 



Styligerous prominences rise in the space between the two wreaths, except in the 

 case of Rhinops ; and in this genus the dorsal side of the corona bears a thick proboscis, 

 around the edges of which the principal wreath is continued. 



In their habits they in the main resemble each other ; for all but Bhinops tolerate 

 even very dirty water, provided that it contains an abundance of the minute organisms 

 on which they feed. 



Genus HYDATINA, Ehrenberg. 



GEN. CH. Body conical, tapering toicards the foot ; foot short, and confluent icith 

 the trunk ; eye absent. 



H. SENTA, Ehrenberg. 

 (PL XIV. fig. 1.) 



Hydatina scnta .... Ehrenberg, Die In/us. 1838, p. 413, Taf. xlvii. fig. 2. 



Cohn, Sieb. u. Ktill. Zeits. Bd. vii. 1856, p. 430, Taf. xxiii. 



Leydig, Mailer's Archiv, 1857, p. 404, Taf. xvi. 



Hudson, Mon. Micr. J. vol. ii. 18G9, p. 22, pi. xix. 



H. senta is one of the largest of the Rotifera, and its flashing styles, lAiddy teeth, and 

 yellow stomach, often stuffed with brilliantly green Euglence, make it a charming object 

 for dark-field illumination. Its shape is conical, the corona being the base, and the 

 toes the apex. When seen, however, from the side (fig. Ib), especially if a little arched, 

 the separation of the head and foot from the trunk is distinctly visible. The styligerous 

 prominences are semi-globular cushions crowned with long and rapidly vibrating styles, 

 set fan-fashion. It is difficult to say how many cushions there are, owing to Hydatina 's 

 incessant restlessness ; but there are probably ten or eleven. Two are on the median 

 line; one on the dorsal edge, and one between the first and the cavity of the head. The 

 rest are arranged round the cavity in a sort of quincunx fashion ; mainly on the dorsal 

 half of the corona. The great hollow in the corona is not only ciliated on its edge but 



