78 CONNECTICUT GEOL. AND NAT. HIST. SURVEY. [Bull. 



13. Chlorophyll cells narrowly trapezoidal or rectangular in 



cross section, free at both surfaces, but with the surface 



walls strongly thickened (Squarrosa, p. 81) 14 



Chlorophyll cells with the free walls scarcely, if at all, 

 thickened; branch leaves erect-spreading* (Cuspidata, p. 

 82) 15 



14. Plants large, monoicous; branch leaves mostly squarrose 



from the middle S. squarrosum 



Plants medium-sized, dioicous; branch leaves more or less 

 imbricated, not squarrose S. teres 



15. Chlorophyll cells triangular in cross section, often enclosed 



toward the inner leaf surface by the hyaline cells 17 



Chlorophyll cells trapezoidal in cross section and free on 

 both surfaces 16 



16. Pores numerous on outer surface of the branch leaves, 



frequently large and usually in rows S. Dusenii 



Pores mostly lacking on outer surface of the branch 

 leaves, when present, small and restricted to the angles 

 of the cells S. cuspidatum 



17. Cortex well differentiated from the central strand 18 



Cortex not well differentiated from the central strand.... 19- 



18. Stem leaves lacerate-fringed at the apex S. Pulchricoma 



Stem leaves toothed at the apex S. Torreyanum 



19. Pores on outer surface of the branch leaves in the apical 



half restricted to the angles of the cells S. recurvum 



Pores on outer surface of the branch leaves in the apical 

 half occurring in the angles and also along the lateral 

 margins of the cells S. parvifolium 



20. Chlorophyll cells enclosed toward one or both surfaces of 



the leaf by the hyaline cells, elliptical or spindle-shaped 

 in cross section; branch leaves squarrose from the 



middle (Rigida, p. 81 ) 21 



Chlorophyll cells free toward both surfaces of the leaf; 

 branch leaves more or less secund or falcate (Sub- 

 SECUNDA, p. 85) 22 



21. Chlorophyll cells elliptical in cross section and enclosed 



toward both leaf surfaces by the hyaline cells 



S. compactum 

 Chlorophyll cells spindle-shaped in cross section and 

 enclosed toward the inner surface of the leaf by the 

 hyaline cells; the outer wall free, but very strongly 

 thickened S, Garberi 



• S. dasyphyllum may be looked for here. 



