506 SYSTEMATIC HISTORY OF THE IKFUSOEIA. 



The members of this family are readily recognized by the stiffness or in- 

 flexibility they display while swimming or when brought into contact with 

 other bodies. The lorica of Prorocentrum and Lagenella is at once perceived 

 to be a distinct covering. When any doubt, however, exists upon this point, 

 a slight degree of pressure upon the specimens placed in an aquatic live-box, 

 or between two slips of polished glass, will easily determine it. The lorica 

 of Trachelomonas Ehrenberg affirmed to be sihcious, and indestructible by 

 fire. Dujardin has a parallel family he names Thecamonadina, consisting of 

 eight genera. These, however, are not the same as the genera of Cryptomo- 

 nadina of Ehrenberg, of which only two are retained, viz. Trachelomonas 

 and Cryptomonas. In the last-named genus are included Cryptoglena and 

 Lagenella, which Dujardin considers have no claim to generic distinction. 

 Prorodon may, he thinks, be the same as his genus Oxyrrhis ; and under the 

 head of Trachelomonas he imites Chcetotyphla and Choitoglena, numbered 

 among the Peridinisea in the classification of Ehrenberg. A new genus, 

 Phacus, is constructed by the same author, to receive those green organisms 

 having a rigid inflexible tunic, which Ehrenberg placed with the flexible and 

 protean EiiglencB. Another group, styled Diselmis, includes many of the 

 Chlamidomonads of Ehi-enberg. Besides these, thi^ee other new genera, viz. 

 Crumenula, Plceotia, and Anisonema, enter into tliis family Thecamonadina, 

 and are described as addenda to the Cryptomonadina of Ehrenberg. The 

 accompanying tabular view represents at a glance the distribution adopted by 

 Dujardin : — 



Thecamonadina. 



_ - .^ 111 f In tegviment hard and brittle... 1. Trachelomonas. 



Body OTOid or globular | Integument membranous. ...... 2. Cryptomonas. 



Body flattened or leaf-like, f With a caudal prolongation ... 3. Phacus. 

 with a single filament \ Without such 4. Crumenula. 



The two filaments equal 5. Diselmis. 



I Body prismatic or navicular ... 6. Plceotia. 

 One flagelUform, one trailing \ Body ovoid, in form of a grape- 1 ^ . „,-e^„^„,« 

 [ seed, with two filaments / ' ' ^"sonema. 



With several filaments { ^'a^^ort^''!^!^.'!!''"^^^^^^ ^^^''^^'- 



Perty borrows from both Ehrenberg and Dujardin, by instituting two 

 families, Cryptomonadina and Thecamonadina, and distributes the several 

 species in another fashion, under new generic names. The distinctive cha- 

 racters of the two famihes are thus set forth : — 



Cryptomonadina. — The surface of the body more or less hardened, but in- 

 separable from the contained substance as a distinct testa. 



Thecamo)iadina. — Possess a distinct red stigma, and, though naked at first, 

 acquire an apparently separable, brittle, silicious shell or testa, having an 

 opening at its fore part for the protrusion of the filaments. In the act of 

 fission the beings (which may or may not entirely occupy the shell) divide 

 into two or four new individuals. 



The Cryptomonadina comprise the genera Cryptomonas, Phacotus, Anisonema, 

 Phacus, and Lepocinclis ; and the Thecamonadina include Chcetotyphla, Try- 

 pemonas, and Chonemonas. 



Cohn (Siebold's Zeitschr. 1853, Band iv. pp. 275-277) sanctions this sub- 

 division of the Cryptomonadina into two families ; for he remarks that Crypto- 



