GENUS SCAPHIDIODON. 751 



vesicles two in number, occupying an antero-posterior position on the right 

 side of the body. Length of body, including spur, 1-240". 

 HAB. Sea water. 



The type of this species and genus as instituted by Stein is the Trichoda navicula 

 of Miiller. The likeness that subsists between this animalcule and the immature 

 condition of Litonotus fasciola is referred to in the account given of that species. 



Fam. III. DYSTERIIDJE, S. K. 



Animalcules free-swimming, more or less ovate, cylindrical, flattened, 

 or compressed, mostly encuirassed, the carapace simple or consisting of 

 two lateral, subequal, conjoined or detached valves ; cilia confined to the 

 more or less narrow and constricted ventral surface; the oral aperture 

 followed by a distinct pharynx, the walls of which are strengthened by a 

 simple horny tube, by a cylindrical fascicle of corneous rods, or by other- 

 wise differentiated corneous elements ; a conspicuous, tail-like style or 

 compact fascicle of setose cilia, presenting a style-like aspect, projecting 

 from the posterior extremity. Mostly inhabiting salt water. 



The representatives of this family were included in Stein's monograph of 

 the Hypotricha,* as a sub-family only of the Chlamydodonta, with which they 

 present many points in common, but are elevated in his succeeding volume,f to 

 the rank of an independent family group for which he retains Dujardin's previously 

 conferred title of the Ervilina, as instituted by the last-named authority for the 

 reception only of the two genera Ervilia and Trochilia. As shown, however, 

 later on see genus sEgyria the name of Ervilia, adopted by Dujardin, had 

 been previously occupied by Turton to denote a genus of Mollusca, and has con- 

 sequently, in common with the family title derived from it, to be expunged from 

 the nomenclature of the Infusoria. While closely allied to the Chlamydodontidse, 

 with which they are most directly united perhaps through the genus Trochilia, all 

 the members of the Dysteriidag may be distinguished by the presence of the 

 peculiar caudal appendage developed at the posterior extremity, and which, with 

 one exception only, takes the form of a pointed spine or style. This caudal spine or 

 style, while rigid in itself, is movable upon its point of attachment as though on a 

 hinge-joint, or rather a cup-and-ball socket, and is utilized by the animalcules for 

 the same purpose as the so-called "foot" or caudal style of the free Rotifera. 

 The aspect of its possessor, indeed, when attached by this point cCappui to any 

 convenient fulcrum of support, fishing for its food with its oral cilia, and turning 

 or bending upon its terminal style as though on a pivot, is so strongly suggestive of 

 certain members of the above-named higher class of organisms, that it is scarcely to 

 be wondered that in certain instances, as, for example, in the case of JDysteria armata, 

 the rotiferal or infusorial affinities of the organisms should have been a matter of 

 dispute. Certain representatives of the Dysteriidae, again, manifest a mimetic 

 resemblance to an entirely distinct organic group. Reference is here made to those 

 genera distinguished by their possession of a bivalved carapace, often variously 

 grooved and sculptured, and which, together with their long projecting ventral cilia, 

 imparts to them, as alluded to in the account of the genus Cypridium, a remarkable 

 superficial likeness to minute Ostracodous Crustacea. No such compound modi- 

 fication of the carapace is as yet known to exist in any of the remaining groups 

 or orders of the Infusoria. The number of specific types referable to the Dysteriidae 



: Organismus,' vol. i., 1859. f Ibid., vol. ii., 1867. 



