PTERODINAD^E. 118 



a distance of about one-third of the axis from the edge of the lorica. From the broad 

 front opening the head protrudes ; and here the cone is slit down a little, and the flaps 

 rounded off, to give the head a freer passage. When the head is withdrawn, the flaps 

 are drawn by muscles close together, up to the under side of the dorsal plate. Just 

 below the pointed end of the conical hollow, there is a circular opening in the ventral 

 plate, through which the foot can be protruded or withdrawn. The gastric glands are 

 very conspicuous. They are unusually long pear-shaped bodies, stretching from the top 

 of the stomach at right-angles to the animal's length, and having their broad heads 

 fastened to the inner lining of the lorica. Bound these points of attachment spread out 

 wide foliations of a filmy substance, curiously and deeply scalloped, and passing upwards 

 towards the head, and outwards nearly to the edge of the shield. It is not easy to see 

 either the lateral canals or the vibratile tags, as they are often obscured by other organs. 

 Lately, however, I succeeded in holding a P. patina firmly down in a clean drop of 

 water, without hurting it ; and, as its head moved backwards and forwards, I could see 

 one of the thick, striped, longitudinal muscles bend aside, and permit a view of two 

 vibratile tags, as well as of the lateral canals to which they adhered. The former lay 

 about midway between the gastric gland and the bottom of the head ; while the latter 

 sloped upwards and inwards, towards the funnel in which the head moved, and were cut 

 off abruptly below by the edge of the gastric gland, at about its middle point : I could 

 see no trace of a contractile vesicle. Two pear-shaped glands are attached by long 

 stalks to the oesophagus just below the mastax, and lower down is a cluster of similar 

 glands crowding round the spot where the oesophagus enters the stomach. The 

 stomach and intestine lie usually side-by-side, and distinctly separate. The latter no 

 doubt discharges through a cloaca at the root of the foot, on its dorsal side, just where 

 it issues from the circular opening in the ventral plate. 1 



Length. Of lorica, -j-^g- inch. Habitat. Clear ponds and ditches : tolerably common. 



P. VALVATA, Hudson. 

 (PI. XXVI. fig. 13.) 

 Pterodina valvata .... Hudson, Hon. Micr. J. vol. v. 1871, p. 25, pi. Ixxii. 



SP. CH. Lorica capable of being folded doivn on each side, nearly circular, smooth ; 

 bosses studding the edge at regular distances ; gastric glands very long, club-shaped, 

 with rounded ends. Lateral foliations inconspicuous. 



I found P. valvata at Abbot's Pond, near Clifton, in the summer of 1871. It was in 

 great abundance, and in company with P. patina ; and in captivity it increased so 

 amazingly, that the glass sides of my aquarium were frosted with the adhering Eotifera. 

 The lorica is remarkably transparent, and is ornamented within its edge with ten bosses, 

 which add greatly to its beauty. When the two species are present together, the differ- 

 ence between them is recognized at a glance ; for, delicate as P. patina is, P. valvata 

 far surpasses it in filmy transparency. While watching some of the new Pterodince, I 

 was surprised to see one of them sailing by with its lorica folded down (fig. 13a) like the 

 flaps of a Pembroke table : 2 its outline was so altered that it scarcely seemed the same 

 animal. This curious infolding of the lorica is due to the contraction of two con- 

 spicuous transverse muscles, which do not necessarily act together ; as a friend, who was 

 watching with me, saw some specimens with only one side folded at a time. 



The gastric glands have not such broad heads as those in patina, and are altogether 



1 Herr Eckstein (loc. cit.) says that the foot is not an organ of prehension, but is the intestine, the 

 ciliated cup being the cloaca. He does not, however, state that he has ever seen the faoces discharged 

 through the foot ; and, indeed, such a statement would seem incredible. Mr. Gosse, however, has 

 witnessed the ffccal discharge, and says : " As well as I could see, it takes place at the upper side of the 

 orifice through which the foot protrudes, projected in a strong current, and not immediately diffused." 



2 [As a rule the folding of the valves is somewhat rarely performed. I have observed, probably, 

 hundreds at various times, and I think I have not seen half-a-dozen folded. -P.H.G.] 



VOL. II. I 



