146 THE AMERICAN MONTHLY [July, 



Figs. =5 and 36. — Stanrastrnni ciinihricitni^ nov. sp. (.S. magnum, 

 tertiam partem longius quam latum, semiccllulis late ellipticis, a vertice 

 triangulare ; lateribus leviter convexis cum spinis velatLs sed paucis ad 

 sinum, multis longioribus ad angulos.) 



Frond rather large, one-third longer than broad, semicells broadly 

 elliptical, end view triangular, with slightly convex sides, beset with 

 spines except at the constricted part, many of which are much longer 

 about the apices of the angles. 



Fig. 6. — Staurastrum cninhricii))i. var. caiiibricuDi^ nov. var. 

 (Var. semicellulis subangularibus et isthmo angustiori.) 



This ditiers from the type by having the semicells somewhat angidar, 

 and the isthmus narrower. 



Fig. 7. — Staicrastrum ostconuin nov. sp. (S. minutum, siiiii latis- 

 simo et obtuso, semicellulis rotundato-ellipticis, a vertice triangulare, 

 angulis rotundatis et lateribus concavis.) 



Minute, front view shaped like a dumb-l)cll, end view trigonal with 

 slightly concave sides, cytoderm smooth. 



Fig. 8. — Staurastrum coarctatuni Breb., var. suhc7irtin)i Nord. 



Fig. 9. — Staurastrum iotaiitmi Wolle. 



This tiny species may easily escape observation. Its arms are simi- 

 lar to those of St. tetraceruni Ralfs, but much finer and more delicate, 

 the end view being also triradiate. Its form in front view is not unlike 

 those of St. O' Me aril Arch., and St. ptcrosporum Lund., but it 

 is smaller, and has arms and not spines. 



Fig. 10. — Arthrodesiuus temiissinius Arch. 



This being a rare species a figure is given here. 



Fig. II. — Staiirastruni ftircatum Ehrb. A faintly punctate variety 

 of this species is shown in the figure. The lateral bifid processes are 

 almost reduced to two spines, the other "■ bifid processes " being sharply 

 bispinate. 



Fig. 12. — As the figures of Staurastrum a7iatinu7n Cooke & Wills, 

 as published by Cooke difter so greatly, a figure of the form which was 

 abundantly seen at Capel Curig, is given. Cooke's figure in Grevillea 

 is nearer the form herein figured than the one in his British Desmids. 

 The extremities of the processes often appear as in Fig. iid., caused 

 by the spines being placed somewhat vertically over each other. 



Fig. 13. — Alicrasterias aniericana Ehrb., var. Lcwisiana nov. var. 

 (Var. lobis polaribus subintegris et latioribus, incisuris angustioribus 

 infra lobos polares.) 



This has the end lobes subentire and wider, the infra-apical incisions 

 are narrower also than in the var. recta Wolle, which it approaches. 

 This is a very distinct variety, and very distant from " forma 7}iajor 

 Reinsch," with which it is worth comparing, as this latter seems to be 

 at the other extreme. 



Fig. 14. — Staurastrum muricatum Breb., var. acutum nov. var. 

 (Var. spinis brevibus (nee granulis), semicellulis truncato-p^ramid- 

 atis.) 



This difiers from the type in the acute though short spines in place 

 of " conic granules," as wellas in the trapezoid or truncately pyra- 

 midal semicells. 



Fig. 15. — Statirastrum opJiiura Lund., forma iionaradiata (Forma 

 a vertice nonaradiata.) End view with nine rays. 



