PTERODINAD A. 113 
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 When the head is withdrawn, the flaps 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plate, through which the foot can be protruded or withdrawn.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. Round 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 esophagus just below the mastax, and lower down is a cluster of similar 
glands crowding round the spot where the wsophagus 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.! 
Length. Of lorica,,1.inch. Habitat. Clear ponds and ditches: tolerably common. 
P. vanvata, Hudson. 
(Pl. XXVI. fig. 18.) 
Pterodina valvata . ‘ ; - Hudson, Mon. Micr. J. vol. v. 1871, p. 25, pl. xxii. 
SP. CH. Lorica capable of being folded down on each side, nearly circular, smooth ; 
bosses stwdding 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 Rotifera. 
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 Pterodine, I 
was surprised to see one of them sailing by with its lorica folded down (fig. 18a) 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 
’ Herr Eckstein (Joc. 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 feces discharged 
through the foot; and, indeed, such a statement would seem incredible. Mr. Gosse, however, has 
witnessed the fecal 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.” 
* [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. Il, I 
