GENUS TETRASELMIS. 315 



of equal length, inserted close together in the centre of the anterior border ; 

 endoplast and contractile vesicle located side by side near the same anterior 

 margin ; parenchyma granular, soft and plastic. Length 1-700". 

 HAB. Fresh water. 



The form of the body of this species, with its bilobate terminal extremity, accords 

 closely with that of the Callodictyon triciliatum of Carter, the number and disposition 

 of the flagella, and shape also of the body, excluding the median groove and 

 posterior bifurcation, approaching that of Tetraselmis. In both of the last-named 

 structural characters it differs considerably from the two preceding species, and would 

 seem almost to lay claim to a separate generic title. In the figures only of this type 

 included in Stein's recently published work, the enclosure within the body of solid 

 food-particles is delineated, but no indication is given of a distinct oral aperture ; 

 probably, as in Callodictyon, these are incepted at any point of the periphery. 



GENUS II. TETRASELMIS, Stein. 



Animalcules free-swimming, solitary, contained within a transparent 

 membranous lorica ; four flagella of similar size and character inserted at the 

 anterior extremity ; endoplasm coloured green, usually enclosing an eye- 

 like pigment-spot. 



Tetraselmis cordiformis, Carter sp. PL. XIX. FIGS. 28 AND 29. 



Lorica somewhat heart-shaped, widest and emarginate anteriorly, 

 rounded and slightly narrower posteriorly; body of animalcule only partially 

 or almost completely fitting the cavity of the lorica, coloured green 

 throughout ; flagella inserted close to each other in the centre of the ante- 

 rior margin and thence protruded through the aperture of the lorica ; eye- 

 like pigment-spot situated near the centre of the lateral border ; a large 

 vacuolar dilatation lying immediately beneath the insertion of the flagella ; 

 contractile vesicles two in number, located one on each side of this area ; 

 endoplast located in the median line, a short distance to the rear of the 

 contractile vesicles ; the posterior region of the body often containing from 

 one to three or more solid corpuscles of an apparently amylaceous nature. 

 Length of lorica 1-933". HAB. Fresh water. 



This species was first described by Mr. Carter * under the title of Cryptoglena 

 cordiformis, and has been rightly recognized by Stein as representing an independent 

 generic form. On one occasion Mr. Carter observed an example that had become 

 encysted and broken up into a number of sporular bodies. The more complete 

 diagnosis of the structural characters of the type here submitted is rendered with 

 the aid of the illustrations of the species given by Professor Stein. 



GENUS III. CHLORASTER, Ehrenberg. 



Animalcules free-swimming, somewhat variable in form, subfusiform, 

 angular, or prismatic ; the anterior border bearing a central vibratile 

 flagellum surrounded by four long, recurved, hair-like or setose flagellate 

 appendages ; endoplasm coloured green, frequently enclosing a red eye-like 

 pigment ; no distinct oral aperture. HAB. Salt and fresh water. 



* ' Annals of Natural History,' 1858. 



