ORDER CILIO-FLAGELLATA. 439 



distinction between the two specific forms only as yet relegated to these respective 

 genera being apparently too slight for generic separation. Excepting for the 

 presence of the second shorter flagellum these animalcules would appear to corre- 

 spond chiefly with those of the monoflagellate form Petalomonas. 



Sphenomonas quadrangularis, Stein. PL. XXIV. FIGS. 21-23. 



Body subfusiform, or quadrangular, twice as long as broad, widest 

 centrally and tapering towards each extremity, divided by four oppositely 

 placed, longitudinal, keel-like ridges, so as to form a quadrate outline in 

 transverse optical section ; longer flagellum stout, nearly twice the length of 

 the body, shorter one slender, scarcely one-quarter the length of the pre- 

 ceding ; endoplast subcentral ; parenchyma transparent, often enclosing a 

 large, ovate, apparently amylaceous body ; contractile vesicle confluent with 

 distal end of the tubular pharynx. Length 1-600". 



HAB. Fresh water ; dividing by longitudinal fission. 



Sphenomonas octocostatus, Stein sp. PL. XXIV. FIGS. 18-20. 



Body symmetrically ovate or subfusiform, compressed, about one and a 

 half times as long as broad, the posterior extremity pointed, the anterior 

 one deeply notched or emarginate ; cuticular surface ornamented with 

 eight longitudinal and sometimes obliquely twisted keel-like ridges ; both 

 flagella slender, the longer one about twice the length of the body, the 

 smaller one about one-quarter the length of the preceding ; endoplasm 

 coarsely granular ; contractile vesicle situated close to but not confluent with 

 the posterior termination of the tubular pharynx ; endoplast subcentral, reni- 

 form, often developing into a large ovate germ-mass. Length 1-400". 



HAB. Fresh water. 



This species is figured by Stein * under the title of Tropidocyathus octocostatus ; 

 in the absence of full descriptive details it appears, however, to accord so closely in 

 all essential points with the type last described, that it has been thought desirable to 

 include it in the same genus. The addition to the Sphenomonas quadrangularis of four 

 intervening longitudinal ridges and the emargination of the anterior border are alone 

 required to produce, in accordance with Stein's figures, an animalcule absolutely 

 identical with the present form. The encysted condition of this species, as 

 shown at PL XXIV. Fig. 20, presents a remarkable resemblance to the carinated 

 seed of an umbelliferous plant, such as Petroselinum or Coriandrum. 



Order VII. CILIO-FLAGELLATA, C. & L. 



Animalcules free-swimming, locomotive appendages consisting of one 

 or more lash-like flagella, and a supplementary more or less highly developed 

 ciliary system ; oral aperture usually distinct. 



As first instituted by Claparede and Lachmann,f this order included only the 

 several genera forming the single family group of the Peridiniidae. The results 

 of more recent investigation have, however, rendered it necessary to extend its 



* 'Infusionsthiere,' Abth. iii., 1878. 



t ' Etudes sur les Infusoires,' Geneva, 1858. 



