MICROSCOPICAL OBSERVATIONS. 37 



6. MicRASTERiA*ARCuATA, B. PI. 1, fig. 6. Quadrangular, Segments tliree-lobed, 

 the basal lobes long and arcuate, subtended by the transverse projections from 

 the ends of the slightly notched terminal lobes. 



An interesting and very distinct species, which can be confounded with no 

 other except the following. 

 Hab. Lakes in Florida. 



7. MicRASTERiAS EXPANSA, B. PI. I , fig. 7. Segments three-lobed, basal lobes 

 long, sub-conical, acute ; terminal lobes slender, forked at the end, with the divi- 

 sions much shorter than the basal lobes. 



This somewhat resembles the preceding species, with which it occurs, but I 

 have seen no intermediate forms, out of many hundreds of each, and the cha- 

 racters above given appear sufficient to separate them. 



Hab. Lakes in Florida, at Pilatka and Enterprise. 



8. MiCRASTERiAS QUADRATA, B. PI. 1, fig. 5. Large, quadrangular, three-lobed, 

 basal lobes elongated, slightly curved, bidentate ; terminal lobes with two slen- 

 der transverse bidentate projections. 



Its larger size and distinctly bidentate projections sufficiently distinguish it 

 from the two preceding species. 

 Hab. Lakes in Florida. 



9. MiCRASTERiAS RiNGENS, B. PI. 1, fig. 11. Obloug, segmcuts three-lobed, 

 coarsely granulated near the edge ; basal lobes subdivided by a deep notch into 

 two rather broad and obtuse or slightly bidentate projections; terminal lobes 

 exserted, emarginate ; extremities bidentate or obtuse. 



Resembles M. Baileyi, Ralfs, but is larger, its divisions less slender, and with 

 the granulations differently placed. 



Lakes in Florida, near Dade's Battle Ground. 



10. Sph^rozosma serratum, B. pi. 1 , fig. 14. Joints broader than long, deeply 

 notched or divided into two transverse portions with acute projecting ends, 

 which give a serrated outline to the chain. 



Common in fresh water in South Carolina, Georgia, and Florida. 



Triploceras, nov. gen. 



Frond binate ; segments straight, much elongated, with numerous whorls of 

 knot-hke projections ; ends of the segments three-lobed ; lobes bidentate. 



A genus closely allied to Docidium, but differing in the three-parted ends of 

 the segments. PI. 1, fig. 9. 



11. Triploceras verticillatum, (Bailey in lit. cum icone 1847, v. Brit. Desmid. 

 p. 219 ) , Robust, with whorls of emarginate projections. Syn. Docidium verti- 

 cillatum, Ralfs. 1. c. p. 219, PI. 35, fig. 9 a, b, d, e. 



Hab. same as next species. 



