CATHYPNAD^J. 97 



however, very thin and flexible, so as to be subject to much inversion in retraction. 

 The head, very freely extruded, is thick and large, a truncate cone, with a slight 

 auricle at each lateral angle, and a central bladder-like lobe, which is retractile. The 

 whole head, which is very mobile, projects between two pointed shelly shields. In 

 death, the head being abnormally extruded, these appear as stout oval (or lozenge- 

 shaped) shields, quite separate from the lorica. The foot, of one apparent joint, is 

 bulbous and kidney-shaped ; to it are jointed the toes, which are much stouter and 

 shorter than in Cathypna luna. They terminate in similar small acute claws, but the 

 shoulders are less sharply angular. It is very thin, viewed laterally (fig. 8a). The 

 dorsal plate comes down to a blunt edge on each side, with feeble duplication ; the 

 hinder ventral parts, inclosed in membrane, being small, and much overlapped by the 

 clear thin edge of the lorica. A very favourable sight of one, as it deliberately turned- 

 up endwise (so slowly, indeed, that I could carefully focus it as it moved), showed that 

 the ventral plate is co- extensive with the dorsal ; but is very thin at the edge, sloping 

 upward toward the middle half ; this forms a downward arch to contain the viscera. 



Herr Eckstein describes the brain in D. Ludwigii, as divided into three long sacs, 

 like as in Copeus centrums and C. Cerberus. In the present species there seems to be 

 a broad base rather abruptly diminished in width, bnt forming only one sac, which 

 carries a great crimson ovate eye, at its very point. 



I have received the species rather plentifully in water from Mr. Hood ; and more 

 sparsely from Mr. Bolton : the former averaging much larger size. Its manners are 

 much more sprightly than those of Cathypna. I have also found it (with lorica very 

 flexible and expansible) in spring, in a domestic aquarium of my own, which had re- 

 mained unchanged for more than a year. P.H.G.] 



Length, T ^ to T ^- inch ; width, ^ to -%}-$ inch. Habitat. Bracebridge Pool, 

 Birmingham : rare. Starmont Loch, Dundee : abundant (P.H.G.). 



D. FLEXILIS, Gosse, sp. nov. 

 (PI. XXIV. fig. 7.) 



[SP. CH. Lorica narrow, nearly parallel- sided, corrugated, flexible, plicate. 



I am not by any means sure that this is entitled to specific rank ; nor, if it is, 

 whether it ought to be placed in the genus Distyla. It may be but the immature con- 

 dition of some other species, such as C. sulcata. Yet the condition, at birth, of the 

 lorica of M. cornuta, appears to forbid the conclusion that flexibility and corrugation 

 are marks of immaturity in this family. A lorica is evidently present, soft and flexible, 

 covered with irregular wrinkles ; marked also with a series of longitudinal folds, scarcely 

 amounting to flutings. The eye is large, rectangular, bright rose-red, seated on the 

 inner side of the brain, close to its point. The other organs are normal. 



Its manners are lively, often wild, searching the edges and surfaces of the water- 

 moss which it haunts, and often creeping within them. It sometimes anchors by its 

 toes, and appears to go to sleep, just like its brothers and cousins. P.H.G.] 



Length. Expanded, ^ inch. Habitat. Sandhurst, Berks (P.H.G.) : rare. 



Genus MONOSTYLA, Ehrenberg. 



[GEN. CH. As Cathypna, but that there is only a single toe. 



This group, consisting of numerous species, is so exactly the counterpart of Cathypna, 

 except for the toe, that one can scarcely avoid the conclusion that this is, structurally, of 

 slight importance. The details of the form, the habits (as the use of tiie toe as a pivot, 

 and the frequent and long-continued inertia), and even the specific variations in the 

 shape of the toe, all are so accurately the reflection of what has been described as to 



VOL. II. H 



