268 
W. E. WADE 
This organism is closely related to an unnamed variety repor- 
ted by Taylor (1985a) in which some of the latéral processes 
are hollow throughout whereas other processes are siinilar to 
the -Michigan speciinens wherein the i)rocesses hâve become 
solidified into stout spines. Taylor’s variety aiso lias a single 
spine on the periphery of the latéral margin Avhereas the Michi¬ 
gan specimens bave two spines on each latéral margin. This 
variety should be conipared with S. forficulatum v. subheleroplo- 
phorum fa. simplex Grônblad {1921 ) and S. forficulatum var. siib- 
beteroplopborum Grônblad (1920) from which it differs in the 
lack of büdy ornamentation except the spines, and in the posses¬ 
sion of distinct apical processes rather tlian spines. 
5. gemelliparum Nordst. Barry and Oakland Counties. 
kS. gracile var. coroimlatum Boldt. Chippewa County. 
S. grallatorium Nordst. Emmet, Roscommon and Schoolcraft Coun¬ 
ties. 
S. grallatorium var. forcipigerum Lagerh. Schoolcraft County. 
grande var. parvum West. Calhoun County. 
S. granulosum (Ehrenb.) Ralfs. Chippewa and Emmet Counties. 
S. gyrans Johnson. Barry County. 
S. johnsonii var. depaiiperatum G. M. Smith. Barry, Oakland and 
Schoolcraft Counties. 
S. muricatum Bréb. Gogebic, Houghton, and Schoolcraft Counties. 
S. natator West. Alger, Barry, and Schoolcraft Counties. 
S. orbiculare Ralfs. Gogebic and Oakland Counties. 
S. orbiculare var. extensum Nordst. Gogebic and Oakland Counties. 
S. orbiculare var. Ralfsii West and W'est. Barry and Mackinac 
Counties. 
S. pilosum (Naeg.) Archer. Gogebic County. 
S. prescoftii sp. nov. (PI. 2, Fig. 8). 
Celliila longior quam lata, semicelliilue transverse ellipticae, in 
apicibus truncatae ; angnlus sinus acutus, extrorsum gradalim 
ampliatus; margines latérales truncati, angiilis levibiis laie 
rotundatis, 8-4 seriebiis transversis granulorum parvorum orna- 
iis: apices ordinibiis rugarum brévium bifidarum ornati. Senii- 
cellulae a vertice visae Iriangulares, marginibus laleralibus redis 
aut paululum concavis, anguli iruncali, apicibus levibiis late 
rotundatis, et 'S-h seriebus transversis granulorum, atqiie, adnw- 
dum inlra seriem concentricam intimam granulorum, pair ruga¬ 
rum lunataruni ornati; ruga iitraque ilepressionem non altam, 
conspicae punctatam introrsus habente. Cellula 20-21 long., 
16-17 [t lat. isthmus 6.5-7 ^ laf. 
Cell longer than broad; semicells transversely elliptic. truncate 
at apices: sinus acute-angled. opening gradually outward; latéral 
