794 ORDER HYPOTRICHA. 



like projection ; ventral styles seven in number, short and thick, centrally 

 disposed ; six stout, scarcely prominent anal styles. Length 1-325". 



Hab. — Salt water. 



From Aspidisca lyncaster, which it would appear to most closely resemble, this 

 form may be distinguished by the presence of three instead of two lateral spur-like 

 projections on the left-hand border ; it is figured and described by Quennerstedt, in 

 company with the preceding type, in Part II. of his ' Sveriges Infusoriefauna,' 1867. 



Aspidisca Andrewii, Mereschk. 



Body elongate-ovate or subreniform, one and a half times as long as 

 broad, rounded at the two extremities, the posterior one being the wider, the 

 right-hand border evenly convex, the left one deeply indented at a distance 

 of one-third of its entire length from the anterior extremity ; the dorsal 

 surface of the carapace traversed by five parallel longitudinal grooves or 

 strise, a triangular or somewhat heart-shaped plate developed on the ventral 

 surface close to the posterior extremity, having its apex directed backwards 

 and reaching to but not projecting beyond the dorsal border of the carapace ; 

 ventral styles very large and short, seven in number, distributed in two 

 rows of four and three styles each ; anal setse long and fine, six in number, 

 four developed in a line to the right and two to the left of the ventral plate. 

 Length 1-480". 



Hab. — Salt water : White Sea, abundant among algae (Mereschkowsky). 



In its possession of six anal setse this species corresponds with the Aspidisca 

 sedigita of Quennerstedt, 



Aspidisca costata, Duj. sp. Pl. XLV. Figs. 25-29. 



Carapace nearly ovate, the ventral portion developed outwards and 



backwards in the form of a triangular plate towards the posterior extremity 



of the left side ; the dorsal surface traversed by six longitudinal furrows ; 



ventral styles as in A. polystyla. Length 1-690". Hab. — Pond water. 



This animalcule is identified by Stein with the Coccudina costata of Dujardin and 

 Perty, and with the Aspidisca cicada of Claparede and Lachmann. The author 

 has on a recent occasion witnessed a highly interesting developmental phenomenon 

 in association with this cosmopolitan species that does not so far appear to have 

 been recorded by any other observer. In pond water abounding with this type 

 there were likewise observed large numbers of a minute, oval, depressed form 

 closely allied to the Glaucojua margaritaceiim of Claparede and Lachmann, which 

 is identified by them with the Cyciidiiim margaritaccuin of Ehrenberg and the 

 Cinctrochilum viargaritacciwi of Perty. The only point of distinction to be discovered 

 in the variety personally examined consisted in the fact that there were three long, 

 hair-like, posterior or caudal setce in place of the single one observed by Claparede 

 and Lachmann. As shown by these last-named authorities, the oral orifice is 

 situated towards the posterior extremity, and has projecting from its aperture a delicate 

 vibratile membrane, described by Stein in Glaucoma sciiitillans as consisting of two 

 separate tremulous flaps, and with which structure that of G. margaritaceiim is stated 

 to coincide. Prolonging the examination of a single individual for a lengthened 

 interval, the author was greatly surprised to notice the gradual appearance, towards 

 the posterior end, of two thick style-like appendages, at first very Aveak and flexible, 

 followed by the development of others both here and towards the anterior extremity, 

 the animalcule shortly becoming transformed through these and the following modi- 



