PTERODINAD A. 115 
the Firth of Tay. I have been able to preserve it in health for many weeks in phials of 
sea-water. Its ovate outline well distinguishes it from lacustrine forms; and this out- 
line is subject to some variation by the action of a stout transverse muscle-band across 
the venter, drawing together the two sides ; the medial length of the ventral plate being 
membranous and flexible, and the pectoral edge being cleft and overlapping. It is well 
suited for illustrating the branchial system. The plexus of the anastomosing afferent 
tubes is wide and particularly clear, and seems to be distributed on all sides of the great 
funnel. And the union of these can be readily traced into a large sac, which (placed on 
the ventral surface) presently bends dorsum-wards into a great pyriform vessel (as in 
P. valvata) on each side, and so pours its deoxygenated water by a slender duct into the 
esophagus. The abdominal viscera are rather small. The long and flexible foot appears 
to be furnished with a central piston which protrudes and retracts its ciliated end ; this 
is endowed with considerable power of adhesion.—P.H.G.] 
Length. Head and foot extended, ,~, inch. Width, 54; inch. Habitat. Among 
conferve in tide-pools ; mouth of the Naze, and of the Tay (P.H.G.): not rare. 
P. TRUNCATA, Gosse, sp. nov. 
(Pl. XXVI. fig. 16.) 
Pterodina elliptica 0 5 : Gosse, Ann. Nat. Hist. 2 Ser. vol. vili. 1851, p. 2038. 
(SP. CH. Lorica ovate, somewhat pointed behind, the occipital edge abruptly trun- 
cate and slightly notched, the pectoral widely cleft. Lacustrine. 
I know this from a single specimen only, which I took in the autumn of 1850, in 
the expanse of water locally known as the Black Sea, at Wandsworth. My study of it 
is imperfect ; for though it rotated freely, I was called away before my observation had 
proceeded far, and when I returned it was retracted and soon died. The eyes are small, 
remote, and almost colourless. The extrusile foot, the trophi, the digestive apparatus, 
the pair of diagonal muscles, and (so far as seen) the plexus of branchial tubules on 
each side, were all generally normal.—P.H.G.] 
Length. Of lorica, +}, inch. Habitat. A lake near London (P.H.G.): very rare. 

Genus POMPHOLYX, Gosse. 
(GEN. CH. Lorica entire, bottle-like ; foot wanting; two frontal eyes; corona 
double behind, united before ; eggs attached after extrusion. Lacustrine. 
Two species, so far as we know, compose this genus; both small, obscure, and rarely 
seen. The one was found by myself in 1850; the other by Mr. Bolton in 1884.—P.H.G.] 
P. COMPLANATA, Gosse. 
(Pl. XXVIL. fig. 1.) 
Pompholyx complanata : 6 Gosse, Ann. Nat. Hist. 2 Ser. vol. viii. 1851, p. 203. 
[SP. CH. Lorica two-sided, nearly circular, with rounded edges ; occipital edge 
obtusely pointed, pectoral edge notched. 
The form is that of a round flat scent-bottle. The corona is composed of two disks, 
resembling those of a Bdelloid, but united in front, with a deep occipital sulcus, wherein 
an antenna protrudes. The eyes are placed one on each side of this sulcus, large, 
globular, ruby-red, and highly refractile. The jaws and alimentary canal seem of the 
Pierodina pattern, but the minuteness of the animal precludes definite observation. 
The cloaca appears at the end of the lorica, as a round orifice, with a slightly raised 
edge around it. Yet the great size of the egg suggests either that this orifice must be 
expansible, or that there must be a separate duct. 
In manners it resembles the Pterodine ; but it revolves as it goes like the Anuree. 
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