256 Mr. J. Ralfs on ihe British Desmiclicce. 



15. Bothriocephulns . Large intestines of skate {Raia Balls). 



, P ^ f Small intestines of little grebe {Podiceps 



\ minor). 



17. . . Intestines of arctic tern (Sterna arctica). 



, o r Large intestines of red-necked grebe (Fo- 



\ diceps rubricoUis). 



appears frona the disposition of the ovaries, but I have never suc- 

 ceeded in detecting the bothrii upon the head ; in fact this part is 

 inclosed in a kind of tubercle which is found upon the peritoneal 

 surface of the pyloric appendages (the body of the animal lying loose 

 in the intestines), and I have drawn this part out to a very tine point, 

 but have not been able to determine its characters. My friend Dr. 

 Drummond has also found this species in abundance in cod taken in 

 the neighbourhood of Belfast. 



* In the intestines of the little grebe (Podiceps minor) I found se- 

 veral specimens of a Bothriocephahis which does not appear to have 

 been described, and which seems to unite the genus Ligula with the 

 Bothriocephalus. It belongs to the first division in Rudolphi's ar- 

 rangement, Inermes, and to the subdivision Dibothrii. The length 

 is from an inch and a half to two inches ; colour when recent red- 

 dish yellow. The head is somewhat subsagittate ; the bothrii, two in 

 number, are placed, one upon the dorsal, the other upon the abdo- 

 minal surface of this part ; they are long, slightly elliptical, or in the 

 form of a simple fissure, extending the whole length of the head and 

 reaching into the articulation next it. There is no neck. The ar- 

 ticulations are broad, rugose, and very short. In the centre of the 

 posterior articulations the circular orifices of the ovaries are seen, 

 from each of which a lemniscus projects, which is long and clavate. 



XXXI. — On the B?-itish Desmidiefe. By John Ralfs, Esq., 



M.R.C.S., Penzance*. 



[With a Plate.] 



Tetmemorus, n. g. 



Frond simple, elongated, straight, cylindrical or subcylindi'ical, 



slightly constricted in the middle ; segments cmarginate at the 



end, but otherwise quite entire. 



I have instituted this genus for the reception of two plants 

 which are placed in Closterium by iVIencghini, but do not well 

 agree with the other species in that genus. 



The fronds are elongated as in C/osterium, from which, how- 

 ever, this genus may easily be distinguished by the cmarginate 

 ends ; the same character and the elongated fronds will separate 

 it from Cosmarium. 



From Euastrum, with which it agrees in the cmarginate extre- 



* Read before the Botanical Society of Edinburgh, April 11, 1844. 



