ANALYSIS OF SPECIES. 



Striae 

 decussate 

 (cutting 



one 



another 



obliquely 



in three 



directions). 



All the 

 strias 

 almost 

 equally 

 delicate. 



Oblique 



striae 

 ci ossing 



one 

 another 



at an 



angle of 



about 



60. 



C Raphe and valve considerably 



sigmoid . . .PI. angulatum. 



Raphe and valve scarcely sig- 

 moid, valve broad, apices 



obtuse 



Raphe and valve scarcely sig- 

 moid, valve very narrow, 



^ apices acute 

 Median oblique striae, flexed 



. PI. rigidum. 







r, 



. PI. intermedium. 

 . PI. afflne. 



Striae 

 rectangu- 

 lar (longi- 

 tudinal 

 and 

 transverse 

 striae 

 cutting 

 one 

 another at 

 right 

 angles). 



Central nodule elongated transversely ; median oblique 

 striae more distant than the terminal . 



Oblique ( Raphe straight, abruptly curved at apices 

 striae 



' Valve with obtuse apices 



crossing 



one 

 another - 



at an 

 angle of 

 more 

 L than 6o. 



Raphe 

 very 

 sigmoid. , 



- Valve with very acute apices 

 Valve with attenuated apices 

 Raphe with a double flexion 



Transverse 



striae 



delicate, 



oblique 



striae 



robust. 



I Valve very large, linear-lanceolate, with sub-obtuse apices 

 Valve rather large, very narrowly lanceolate, with acute apices 



PI. naviculaceum. 

 PI. speciosum. 

 PI. elongatum. 

 PI. acutum. 

 PI. naviculaceum. 

 PI. marinum. 



PI. formosum. 



PI. decorum. 



Frustules 



not 



enclosed 



in mucous 



tubes. 



f In brackish water : Valve short, lanceolate, apices 



broad, longitudinal striae 10-11 in 1 c.d.m. . PI. Hippocampu3. 



Longitudinal 

 strias further 

 apart and conse- j Marine : Valve short, apices narrow, 7-9 longitu- 

 quently more dinal striae in 1 c.d.m. 



' e 



Fresh water : Valve elongated, narrowly lanceo- 

 late, 10-11 longitudinal striae 



Marine : Valve linear, very elongated 



visible than the 

 transverse. 



Longitudinal 



and transverse 



striae equally 



distant. 



PI. littorale. 



PI. altenuatum. 

 . PI. Balticum. 



Fresh water : Valves lanceolate-sigmoid 



PI. acuminatum. 



Longitudinal 



striae more 



approximate and - 



less visible than 



the transverse. 



' Valve very large, transverse striae 



Apices not 



rostrate 

 produced. 



. PI strigilis. 



narrow 



. PI. Spencerii. 



Apices 



rostrate 



produced. 



very distant, robust 



1 Valve linear - lanceolate, 

 (more than 1 c.d.m. ) 



I Valve linear, excessively narrow (less 



^ than 1 c. d. m. ) . .PI. tenuissimum. 



Fresh water : Valve broadly lanceo- 

 late, rostrum rather broad . PI. Parkeri. 



Marine : Rostrum broad and short, 

 striae very fine . . PI. distortum. 



Valve linear-lanceolate ; 



Marine. 



Rostrum 



very 



apices very rostrate . PI. Fasciola. 



Valve very linear-lanceo- 

 late ; apices extremely 



rostrate 



Rostrum 

 apices 



PI. macrum. 



inflated at 



PI. reversum. 



f Valve very obtuse ; raphe appearing strongly 



sigmoid 



. PI. exiruium. 



Frustules enclosed in mucous 

 tubes, valves short, stubby 



, Valve obtuse ; raphe appearing gently sigmoid . PI. scalproides, 



