362 ORDER CHOANO-FLAGELLATA. 



described genus Spongomonas. The single species left out of these two, to which 

 another is now added by Stein, was recognized by Cienkowski as exhibiting a 

 pecuhar beak-hke modification of the anterior region, into which the base of the 

 single flagellum is inserted. Professor James-Clark was the first to indicate the 

 probable homology of this beak-like prominence with the collar-like organ dis- 

 covered by him in connection with the two generic forms Codosiga and Salpingxca, 

 his inference being entirely substantiated by Stein's later illustrations. As shown in 

 the figures reproduced from this authority, the collar-like organ or its homologue in 

 the present genus, so far as observed, never exhibits that expanded funnel-shaped 

 contour which is seen in all the Choano-Flagellata previously described, but exhibits 

 rather that conical form with a wider basal or proximal, and narrower contracted 

 distal region, that characterizes them in their retracted state. Whether or not a cir- 

 culating current or cyclosis of the sarcode substance of this reduced and rudimentary 

 form of collar developed in Fhalansterium, is maintained, remains to be demon- 

 strated. 



As first pointed out by Professor H. James-Clark, the habit exhibited by the 

 members of this genus of exuding and socially inhalDiting a common gelatinous 

 matrix or zoocytium, approximates them more nearly than any previously known 

 members of the independent collared Flagellata to the important group of the 

 Spongida. An advance in this direction is nevertheless accomplished in the recently 

 discovered Flagellate type upon which the new generic title of Frotospongia is here 

 conferred. 



Phalansterium consociatum, Fres. sp. Pl. XII. Figs. 5-9. 



Common gelatinous matrix or zoocytium depressed, discoidal or shield- 

 shaped, more or less granular, divided by radiating dissepiments into 

 separate subtriangular or tubular areas representing the chambers within 

 the zoocytium primarily constructed by the individual zooids ; contained 

 zooids elongate-ovate or pyriform, from one and a half to twice as long as 

 broad ; collar conical, having the appearance of an anteriorly developed 

 beak-like process, about one-third the length of the body ; contractile 

 vesicles two in number, posteriorly located ; endoplast spherical, subcentral. 

 Length of zooids 1-2500", diameter of discoidal zoocytium 1-420". 



Hab. — Fresh water. 



This species was originally described by Fresenius* under the title of Monas 

 cojisociatnm, its relegation to the present generic group being accomplished, as already 

 remarked, by Cienkowski. The zooids in their encysted condition, as reported by 

 this authority, exhibit, as shown at PI. XII. Fig. 8, a somewhat peculiar contour, 

 being subspheroidal with three longitudinal keel-like ridges, one of which is produced 

 in a mucronate manner at the two apices. According also to this observer, fission 

 in this type takes place longitudinally, or in a direction contrary to that which, as 

 indicated by Stein, obtains in the species next described. 



Phalansterium digitatum, Stein. Pl. XII. Figs. 1-4. 



Animalcules plastic and variable in form, ovate or elliptical, one and a 

 half to three times as long as broad, building up an erect, lobate, palmate, 

 or digitiform, subdichotomously branching, coarsely, granular zoocytium ; 

 terminations of the branches hollow, inflated, and subcylindrical, with large 

 circular distal apertures, containing each a single or, after fission, two 



* ' Beitiage zur Kenntniss Mikroskopischer Organismen,' Frankfort, 1858. 



