100 Clark — Holophytic Plankton of Lakes Atitlan and Amatitlan. 



19. Staurastrum gracile Ralfs. 

 Staurastrum gracile Ralfs, Ann. Xat. Hist. 15; 155, pi. 11, f. 3, 1845; 



Wolle, Desm. U. S., 133, pi. XLIII, figs. 1(3, 17, 1884. 



Not common, but single individuals were frequently found scattered 

 through the other plankton-algae of Lake Amatitlan. A few examples 

 were observed dividing. Our average specimens have a length of 40m, 

 and length of arm 50m. 



20. Staurastrum evermanni Clark sp. nov. 



Diagnosis: End view a slender, long-armed triangle with concave sides; 

 main axis of the body slender, enlarged into bulbous swellings at the 

 junction of the semi-cells; chloroplasts 1 night green, regular, following 

 the general form of the group; periderm prickly; length of individual 

 arms from center of body about 55m; length of the long arms of the H- 

 shaped figure formed by the desmid in side view 110m; length of axis 40m, 

 its average width 10m ; arms each ending in stout diverging spines ; asexual 

 reproduction of the species, frequent in the material at hand, and, as usual 

 in the group, by the formation of new semi-cells joining the old. Type 

 material, plankton sample No. 14, collected at a surface towing in front of 

 Hotel Laguna, Lake Amatitlan, Guatemala, February 5, at 9 p. m. by 

 Dr. Seth E. Meek. 



The type material will be deposited in the U. S. National Museum. 



This species is very common in some of the plankton, nearly all the 

 samples containing a few plants, and the type sample contained it in 

 marked abundance. In end view this desmid almost exactly resembles 

 S. pseudobaldi Wille, as figured by Wolle (Desm. U. S., pi. XLVI, fig. 

 9), and the side view is more like that of S. macroccrum Wolle (figured 

 in Desm. U. S., pi. XLIII, fig. 4) than any other species of which 1 can 

 find figures. It differs from that species, however, in the arms being 

 more nearly straight and more slender, and particularly in the elongate, 

 slender body, the ends of which terminate at the junction of the semi- 

 cells in a well-marked bulb-like expansion. I take great pleasure, in 

 naming this attractive species for Dr. Barton Warren Evermann, of the 

 U. S. Bureau of Fisheries. 



Order DIATOMACE.E. 

 21. Epithemia turgida (Ehrenberg). 



Navicula turgida Ehrenberg. Phys. Abh. Akad. Wiss. Berlin, 1830, 64, 



L830. 

 Epithemia turgida Griff . and Henf. Mic. Diet. 299, pi. 1<>, fig. 32, 1883, 



Wolle, Diatom, X. A., pi. XXXV, figs. 10-13, 1890, Van Heurck, 



Treat. Diatom. (Baxter trans.), 294, fig. 66, and pi. 9, fig. 346, L896; 



Stokes, A.piat. Mic. 94, fig. 70, 1896. West, Brit. F. W. Alg., 300, fig. 



L42, L904. 



Rather rare, only occasional specimens having been seen in the 

 gatherings. 



