6 Rhodora [JANUARY 
but bordered by a series of imbricated, hyaline scales. "The spores 
in the two American species afford the best differential characters 
in separating them from R. lamellosa, in which a distinct wing is 
developed at the junction between the convex face of the spore and 
the three plane faces. The absence of a wing in the American plants 
which had been referred to R. lamellosa was first pointed out by Under- 
wood.' The spores in the true R. lamellosa are further distinguished 
from those of R. Austini by their slightly larger size (90-120 u accord- 
ing to Müller ?) and by the fact that all four faces are reticulated. In 
R. americana, also, the spores are larger than in R. Austini, measuring 
90-126 u according to Howe, and the meshes of the convex face are 
likewise larger, averaging about 15 u in width. The thallus has even 
more conspicuous scales than in the eastern plant and is slightly more 
robust, measuring 2.5-4 mm. in width. Howe’s figures of R. ameri- 
cana should be carefully consulted in studying R. Austini. 
3. Riccra picryospora M. A. Howe, Bull. Torrey Club 28: 163. 
1901. On moist black earth in a path among rocks, in company with 
R. sorocarpa and Grimaldia fragans. West Rock Ridge, Woodbridge, 
Connecticut (4. W. E.). New to New England. Known from only 
two other stations, namely: Athens, Georgia (H. M. Harper), the 
type locality, and Glencoe, Missouri (N. L. T. Nelson). A portion 
of the original material, kindly communicated by Howe, agrees 
closely with the specimens from Connecticut, except that the spores 
are a little larger. 
In R. dictyospora the color is a more decided green than in either 
of the preceding species and is only slightly glaucous. The plants 
sometimes form irregular rosettes 1.5-2 cm. in diameter but are much 
more likely to grow in intricate mats or irregularly scattered. The 
thallus is narrow, measuring about 1 mm. in width, and the branches 
are mostly 2-3 mm. long. They tend to spread less widely than in 
most species of Riccia. The terminal branches have rounded or 
slightly emarginate apices. Near the tip a narrow median sulcus 
can be demonstrated, but this extends backward for a short distance 
only, the older parts of the thallus being plane or nearly so on the 
upper surface. The thallus is destitute of marginal hairs but bears 
a series of ventral scales, which extend slightly beyond the margin. 
These are usually deeply pigmented with purple and form a narrow 
! Bot. Gaz. 19: 274. 1894. 
? Rabenhorst's Kryptogamen-Flora 6: 187. 1907. 
