GENUS PERIDINIUM. 449 



like indurations, which bound the equatorial and vertical furrows. The elegant 

 sculpturing of the larger polygonal and usually five- or six-sided facets, may be most 

 readily examined in connection with the empty or disintegrated carapaces that are 

 usually found abundantly distributed in the water that supplies the living zooids. 

 A delineation of such a highly magnified single facet is given at Fig, 3. The encyst- 

 ment of this species within its cuirass has been observed by Claparbde and Lach- 

 mann, as also tlie naked Gymjiodifiium-\\kQ phase, both of these conditions being 

 reproduced from their drawings at Figs. 4 and 5, In examples examined by the 

 author, a long curved band-like endoplast or nucleus, similar to that commonly met 

 among the Vorticellidce, has been occasionally observed, one such distinctly nucleated 

 specimen being represented at Fig. 56. The species has been obtained by the author 

 in profusion from various localities in the suburbs of London, and has also been 

 received from the neighbourhood of Birmingham, through Mr. Thomas Bolton. 



Very recently, November 1880, the author has received this animalcule in com- 

 pany with other Flagellata, through Mr, John Hood, from the neighbourhood of 

 Dundee, The chief interest attached to such consignment is connected with the fact 

 that many lunate encystments, corresponding essentially with those first described of 

 an unknown form by Clapar^de and Lachmann, and represented at PI, XXV. Figs. 

 49 and 50, were detected among the sedimentary matter at the bottom of the phial in 

 which they were transmitted. The contents of these cysts, which were usually 

 divided into two equal moieties, exhibited the same rust-brown hue as the motile 

 zooids. There can be but little doubt that the similar shaped encystments in the 

 figures quoted belong to the present very widely distributed species, 



Peridinium apiculatum, Ehr, sp, Pl. XXV. Figs, 6 and 7. 



Body oval, depressed ; cuirass composed of large polygonal reticulate 

 facets, the edges of which are finely hispid and separated from one another 

 by clear, smooth intervals ; colour yellowish-green ; an eye-like pio-ment- 

 spot of oblong form usually present. Length 1-570" to 1-350". 



Hab. — Fresh water. 



This species was described by Ehrenberg under the title of Gymnodiniwn apicu- 

 latJini, and does not so far appear to have been encountered by any other authority. 

 Stein is inclined to regard it only as a variety or older phase of Feridi?imm 

 tabulatwn. 



Peridinium reticulatum, C. & L. Pl. XXV. Fig, 41. 



Body ovoid ; cuirass composed of numerous minute, smooth, polygonal 

 facets, equatorial furrow obliquely developed ; colour brown. Length 

 1-570". Hab. — Salt water : Norwegian coast (C. & L.). 



Peridinium spiniferum, C. & L. Pl. XXV. Figs. 15 and 16 



Body ovoid, rounded posteriorly ; cuirass composed of large polygonal 

 facets ; two closely approximated spines developed at the apical extremity 

 of the anterior segment ; transverse furrow very oblique, forming an elongate 

 spire. Length 1-620". 



Hab. — Salt water ; Norwegian coast (C. & L.), 



Peridinium splendor-maris, Ehr. 



Cuirass ovate or subglobose, transparent, facetted, cribrate or granular, 

 neither apiculate nor provided with horn-like processes ; margins of the 



2 G 



