226 CusHMAN : Zygospores of desmids 



as C, orbiculatunt (Memor. R. Accad. Sci. Torino II. 28 : 1 1 

 (107). //. 7,/. 4.6-4,8. 1877), agreeing exactly in form and size. 

 The form of the semicells is more oval in front and end view than 

 in Ralfs' species and may in this way be best distinguished. But 

 the zygospore is very different, holding a place distinctly apart 

 from the usual type of Cosmanum zygospore. That of C. orbicu- 

 latum is spherical with the usual type of short conical spines. In 

 the present species it is a decided oblate spheroid, on one end 

 evenly convex, on the other concave in the middle forming a dis- 

 tinct pit of considerable size. The zygospore has from sixteen to 

 twenty lamellar plates extending from pole to pole, evenly scal- 

 loped, each plate with about ten spines broadly elliptical at the 

 base, becoming circular at the broadly truncated apex. The 

 portions between the lamellae are indistinctly striate. Altogether 

 this forms a very curious type of zygospore for this group. 



Long. 40/^, lat. 28//, lat. isthm. 6.5//, crass. 21.5 /i. 



Long. zyg. c. sp. 34/i, lat. zyg. c. sp. 50//. 



Common in fruiting condition at Pondville, Mass. 



■ 



Sphaerozosma readingensis sp. nov. Plate 7, figures 10, \oa. 



Sphacrozosnm, smooth, without exterior ornamentation, sinus 

 deep, somewhat gaping, end view broadly elliptical, semicells in 

 side view nearly circular, in front view nearly three times as wide 

 as long ; cells connected by two glandular processes with a third 

 projection between them in the middle of the end of the semicell 

 {Jig. loa). 



Zygospore much like that of S. Aiihertianum figured by W. 

 and G. S. West, wath fairly long acicular spines. 

 Lat. cell. 28/-/, long. 22 fi, lat isthm. 6.5 fx. 



» 



Lat. zyg. s. sp. 25 /i, lat. zyg. c. sp. 52 ^«. 

 Common in the collection from Reading, Mass. 



Staurastrum brevispinum Breb. Plate 8, figures 12, 13. 



\\\ figure 12 is shown an early stage in the formation of the 

 zygospore. There is a central mass, green in color, surrounded 

 by an outer hyaline covering. At the stage figured this consists 

 of two distinct portions, the inner one of which evidently becomes 

 the main wall of the zygospore, while the outer one is used up in 

 the development of spines. 



