OF THE PROTOZOA. OPALIN.EA. 271 



On turning to the systematic descriptions of various writers, we find much 

 discrepancy in detail, and much difference in opinion, respecting both the 

 species to be counted among Opalincea and their generic distribution. 



The family ' Leucophryens ' of Dujardin, and the CobaUna of Perty, severally 

 include most of the species which we would reckon as Opalincea. These, in 

 Ehrenberg's system, were scattered through several genera, — the majority, 

 however, being comprised in his genus Bursaria. Stein points out three prin- 

 cipal modifications of form, but is not prepared to constitute them into genera. 



In the classification adopted by the three first-named writers, the Opalincea 

 were accounted ordinary Ciliated Protozoa. Perty and Dujardin so far re- 

 cognized their peculiarities as to erect them into a distinct family. Siebold 

 went ftiriher, and, on account of the absence of a mouth, placed them, with 

 Astasia^a and Peridinicea, among the Astoma. We coincide with Siebold in 

 thus more completely separating them from the stomatodous Ciliata than the 

 other authors named, but at the same time look upon them as more nearly 

 allied ^vith Ciliata than with either Peridinicea or Astasicea, and consequently 

 prefer to treat the Opcdinoia as a subgroup of those Protozoa. 



Neither the intimate stnicture, nor the developmental histoiy of the Opa- 

 lincea, is sufficiently well understood for them to be arranged in well-defmed 

 genera ; nevertheless, as both Dujardin and Perty have each essayed a sy- 

 stematic distribution, it behoves us to set their schemes before the reader. 



Dujardin divides the Leucophryens into three genera, viz. Spathidium, 

 Leucophrys, and Opcdina. Besides these, he has other mouthless genera in 

 his family Ploesconiens, viz. Diophrys and Coccudina, maiine but not parasitic 

 animalcules ; also a genus Trochilia without distinct mouth, also marine in 

 habit, located in the family Erviliens ; and last, the genua Plagiotoma, among 

 the Bursariens, parasitic in habit, and supposed to have a mouth situated at 

 the bottom of a fossa, but which contained no foreign matters, and could not 

 be fed artificially with colouring matter. Of these genera Coccudina, Dio- 

 phrys, and Trochilia are imperfectly kno^vn, particularly the two last, and 

 the absence of a mouth cannot be predicated of them with any certainty, — 

 whilst of the last named {Plagiotoma) the balance of evidence is against the 

 existence of a mouth, and, as we shall see, this genus is a member of Perty's 

 family Cohcdina, and has, moreover, in Stein's opinion, no claim to rank as a 

 distinct genus. 



The parasitic family Cohcdina, Perty, comprises the genera Alastor, Plagio- 

 toma, Leucophrys, and Opcdina. The characters of these several genera, placed 

 by observers among the Opcdincea, or some parallel group, together with their 

 mutual relations and differences, will be fuUy treated of in the systematic 

 section of this work. 



FAMILY II.— PERIDINI^A. 

 (Plate X. 224-226; XXXI. 16-23.) 



This family, in Ehrenberg's classification, comprehended four genera, viz. 

 ChcetotypJda, Chcetoglena, Peridinium, and Glenodinium ; but, as Dujardin 

 rightly judged, the two first genera belong rather to the Cryptomonadina, by 

 being destitute of the ciliary furrow, the leading characteristic of the Peri- 

 dinicea. Our description ^viU therefore particularly apply to the two other 

 genera, Peridinium and Glenodinium. 



The beings imder consideration have received little attention from natu- 

 rahsts, and are stiU imperfectly imderstood. Indeed, we feel that no sufficient 

 data are at hand whereon to ground an opinion relative to their true position, 

 nature, and affinities. We place them here as a supplementary group of 



