GENUS THURICOLA— COTHURNI A. 719 



Seen from either a front or dorsal aspect, and viewed with insufficient magnifying 

 power, the complex mechanism which here takes the place of the simple valve of the 

 form last described, presents the appearance, indicated at PI. XL. Fig. 6, of two 

 oppositely opposed arcuate cusps. It is under these conditions that the author has 

 been able to establish its identity with the Vortkdla folliailata of O. F. Miiller. 

 Viewed again in profile, its aspect corresponds so closely with that of the ovate 

 valve of Thurkola valvata that it is scarcely to be distinguished from that form. 

 Examined with a power of 600 or 800 diameters, the comb-like character of the 

 valve is, as shown at PL XL. Figs. 7 and 8, verj' clearly demonstrated, and when 

 once recognized, may be easily defined with a much lower power. The author has 

 obtained this type abundantly in pond water in the neighbourhood of London, and 

 has likewise received it through Mr. Thomas Bolton from Stourbridge, Worcester- 

 shire. An animalcule in no essential points distinguishable from the fresh-water 

 species has been obtained by the author in salt water at Bognor, Sussex. 



Thuricola operculata, Gruber sp. Pl. XL. Figs. 13-15. 

 Lorica sessile, transparent, subcylindrical, slightly constricted towards 

 the anterior border, over three times as long as broad, one side of the 

 anterior margin developed greatly in advance of the other ; valve or oper- 

 culum circular, attached to the lorica by a delicate membranous ligament, 

 which is continued down one side and joined to the base of the animalcule's 

 body ; animalcule slender, subcylindrical, projecting when fully extended 

 for nearly half its length beyond the aperture of the lorica, its cuticuiar 

 surface finely striate ; transversely attached basally to the lorica through the 

 medium of a distinct footstalk. Dimensions and habitat unrecorded. 



This species differs essentially from Thuricola valvata in the uneven or emarginate 

 contour of the anterior border of the lorica, in the usually more slender proportions 

 and greater extensility of the enclosed animalcule, and in its mode of fixation 

 through the medium of a separate footstalk to its excreted domicile. The data 

 recorded by Gruber relating to the opercular structure, in describing this animalcule 

 under the title of Coihiirnia operculata* are of high interest, and are thus sum- 

 marized : " In empty loricoe the operculum is always open, so that its closure must 

 be due to the contraction of the animal. There is, in fact, attached to its under 

 surface, one end of a delicate cuticuiar membrane (PI. XL. Figs. 14 and r5, r /), 

 bent longitudinally into a long cylinder, and with its other end embracing the 

 proximal extremity of the animal. When the latter retracts, the membrane is pulled 

 upon and the operculum closed. The membrane is so delicate that under ordinary 

 circumstances all that can be seen of it are its edges, which look like two 

 delicate threads passing from the base of the animal to the operculum." It will 

 probably be found that a similar delicate membrane connects the operculum with 

 the body and fulfils a similar function in the preceding species. 



Genus XIV. COTHURNIA, Ehrenberg. 



Loricse erect, attached posteriorly to their basis of support through the 

 medium of a conspicuously developed pedicle; animalcules, as in Vagi- 

 nicola, either adherent in a sessile manner to the posterior extremity of 

 the lorica, or fixed to the same by a continuation from without of the 

 external supporting pedicle. Inhabiting salt and fresh water. 



* ' Zeit. Wiss. Zoo!.,' Bd. xxxiii., p. 439, 1879. (Translation in 'Journal of Royal Micro- 

 scopical Society,' April 1880.) 



