270 GOMPHONEMA. 



space. Median stria; dividing dichotomously, and consequently appearing 

 alternately long and short. Length, about 9 to 12 c.d.m. Breadth at median 

 portion, about 3*5 to 4 c.d.m. 



Fresh water. England (Kitton, Comber). Wales (Ralfs) ; in the Mountains of Scotland, 

 Ireland, Scandinavia, etc. 



G. constrictum Ehr. (Abh., 1830; h.v.h. Atl., pi. 23, f. 6* ; 



Type No. 205), plate 7, fig. 296. 



Valve cuneate, strongly inflated at median portion, with lower apex narrow, 

 margins almost parallel, slightly cuneate, upper apex broad, deeply constricted 

 at the middle, and forming thus an apex broadly capitate, truncate, rounded. 

 Raphe surrounded by a rather broad hyaline zone. Terminal nodules not 

 reaching to the apices. Stria; radiate, alternately long and short round the 

 central nodule, robust, finely divided transversely, 10 to 12 in 1 c.d.m. Length, 

 about 4 to 6 c.d.m. 



Fresh water. Rather common, everywhere. 



var. capitatum. (G. capitatum Ehr. ; H.V.H. Atl., pi. 23, fig. 7*), 

 plate 7, fig. 297. 



Differs from the preceding by the constriction on the upper portion of 

 the valve being absent or very slight. 



Fresh water. Less common than the preceding. 



forma curta. (H.V.H. Atl., pi. 23, f. 8*; Type No. 206), plate 7, 

 fig. 298. 



Differs from the preceding by its short thick-set form (2 to 3 c.d.m.), 

 and the triangular form of the lower portion of the valve. 



Fresh water. Rather frequent. 



II. Median stria? not alternately long and short. 



I. No large rounded hyaline area. 



a. VA1JVR WITHOUT A MORE OR LESS STAURONEIFORM HYALINE 

 AREA IN THE MEDIAN PORTION. 



b. Valve not lanceolate-rostrate. 



C. UPPER APEX APICULATE. 



G. acuminatum Ehr. (inf., p. 217, n. 308, pi. 18, f. 4; H.V.H. 



Atl., pi. 23, f. 16*); in Types Nos. 10, 18, etc., plate 7, fig. 299. 



Valve cuneate, inflated in the middle, lower part with almost parallel 

 margins, slightly constricted in the median portion ; upper apex dilated, 



