264 TROPIDONEIS. 



var. pusilla. (A. pusilla Greg. ; Diat. of Clyde, p. 32, pi. 4, f. 56, 

 56$ ; in Type No. 74, very rare), plate 29, fig. 804. 



Differs from the type form by its smaller size (4 to 6 c.d.m.), and its 

 more approximate stride (24 in 1 c.d.m , according to Gregory). 



Marine. Rare: Blankenberghe (H.V. H. ), Braydon, Norfolk (Kitton), Bangor (Stolt.), 

 Loch Fine, Scotland (Greg.), Ireland (O'Meara). 



In his Diatoinacete of the Clyde (p. 33), Dr. Gregory refers to his A. 

 lepidoptera a singular form which he figures as plate 4, fig. 59^ and 60. The 

 same form has been figured by Dr. Ad. Schmidt (Nordsee, pi. 3, fig. 1*), under 

 the name of Amphiprora obtusa (plate 29, fig. 803 of this work), and by Mr. 

 Cleve (N.R.D. and Arct. Diat.), under the name of Naviatla arctua CI. 



In his Synopsis Prof. Cleve has erected it into a special genus, under 

 the name of Pseudo-amphiprora. The form we refer to P. stauroptera, has 

 its valves elliptic-lanceolate, with obtuse apices, a moderately broad stauros 

 and striae fine (14 to 18 in 1 c.d.m.), punctate, parallel, and crossed on each 

 side of the raphe by an arcuate line, somewhat constricted near the stauros. 

 Length of the valve, n to 13 c.d.m. Breadth, 3 to 3^5 c.d.m. 



Marine. North Sea (Greg. ) ; Finmark (Cleve). 



O. maxima Greg. (Diat. of Clyde, p. 35, pi. 4, f. 61 \ h.v.h., 

 pi. 22, f. 4-5*), plate 5, fig. 288. 



Valve lanceolate, very slightly attenuate as far as the sub-acute apices, 

 deeply depressed at the median portion, showing a robust arcuate ala on each 

 side of the raphe. Striae about 14 in 1 c.d.m., leaving a stauroneiform area 

 round the central nodule ; distinctly punctate, puncta forming longitudinal 

 lines. Frustules rectangular, very broad, with apices rounded, deeply 

 constricted at the median portion. Length, 11 to 16 c.d.m. 



Marine. Not yet found in Belgium. England (Kitton), Scotland (Greg. ), Ireland (O'Meara), 

 Heligoland. 



Sec. II. PLAGIOTROPIS Pfitz., i 87 i. Valve with raphe eccentric, 

 girdle face very feebly or not constricted. 



ANALYSIS OF SPECIES. 



f Frustules f Lateral plait conspicuous throughout 



slightly the length of the valve . . PL elegans. 



Valve with constricted \ 



margin J at the median j Lateral plait only well marked on the 



flexed portion. l_ terminal third of the valve . . PI. Van Heurckii. 



regularly. 

 t Valve with margin abruptly gibbous-inflated at the median portion . PI. gibDerula. 



Frustule without any constriction, only differing from a 

 Nitzschia by the central nodule . . .PI. vitrea. 



