GENUS P LAC US. 489 



Loxocephalus luridus, Eberhard. Pl. XXXIL Fig. 16. 



Body elongate-ovate, subcylindrical, three times as long as broad, 

 widest centrally, tapering gradually towards the two extremities ; the 

 oblique anterior constriction bearing on the side nearest the apical ex- 

 tremity two short, conspicuous, adcurved setae ; four long, straight, hair-like 

 caudal setae developed from the posterior termination ; endoplast sub- 

 spherical, situated in the median line at a distance of one-third of the entire 

 length from the anterior extremity ; endoplasm granular, very dark and 

 opaque. Length 1-75". Hab. — Infusions with vegetable matter. 



This species is figured and described by Dr. Ernst Eberhard in the 'Oster- 

 Programm der Herzogl. Realschule zu Coburg' for the year 1862. 



Loxocephalus granulosus, S. K. Pl. XXVI. Fig. 47. 



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

 broad, widest posteriorly, the anterior end curved slightly towards the left, 

 the oblique anterior constriction bearing on each side, as viewed from a 

 dorsal aspect, a single, short, adcurved seta; a single, straight, hair-like 

 caudal seta projecting from the posterior termination ; contractile vesicle 

 situated in the median line at a distance of one-third of the length of the body 

 from the posterior extremity ; cilia short and fine throughout ; parenchyma 

 coarsely granular, dark and opaque. Length 1-428". 



Hab. — Marsh water with decaying vegetation. 



The animalcule connected with the above title was obtained by the author in 

 some abundance in marsh water from Le Marais, Jersey, November 1878, in com- 

 pany with Spirostomum ambigimm, Paramecium aiirdia, tlroccntncm turbo, Pleuronema 

 chrysalis., and other pond-frequenting types. The general contour, as seen with 

 moderate magnification only, agrees so closely with that of Colpidium or Pleurochili- 

 dium, that at first sight the desirability of referring it to one of these two genera was 

 anticipated. On closer examination, however, it was found to be entirely wanting 

 in the special oral structure that distinguishes these latter. No trace of an undu- 

 lating membrane or of a pharyngeal passage could be detected, Avhile even with a 

 magnification of eight hundred diameters the position of the oral aperture in the 

 antero-ventral region could be predicated only by the more active ciUary vibration at 

 that point. The two short adcurved setje projecting from the anterior constriction, 

 accompanied by the presence of a long hair-like posterior seta, demonstrate that we 

 have here an animalcule closely allied to the Loxocephalus luridus of Eberhard, but 

 from which, as a species, it may be at once distinguished by its considerably smaller 

 size, and by the diverse number and disposition of the setose appendages. When 

 disturbed the animalcules swim to and fro in a straight fine with considerable 

 rapidity, but otherwise remain quiescent in some selected spot, numerous examples 

 being often found in close proximity. In consequence of the dense granular 

 character of the endoplasm, some difficulty was experienced in ascertaining the 

 position of the contractile vesicle and endoplast. 



Genus III. PLACUS, Cohn. 



Animalcules free-swimming, ovate ; cuticular surface indurated, reticu- 

 late; oral aperture inferiorly situated ; fine, short, vibratile cilia distributed 

 throughout the cuticular surface, none of a specialized character in the 

 neighbourhood of the mouth ; endoplast and contractile vesicle conspicuous. 



VOL. II. C 



