Mr. W. H. Dall on Deep-water Limpets and Chitons. 11 
yet they have hitherto always shown some character which 
has necessitated their being kept separate *. 
EXPLANATION OF PLATE I. 
Eusphenopteris tenella, Brong. 
Fig. 1. Portion of barren frond from Sauchie, near Alloa. . 
Fg. 2. Portion of larger form from same locality. 
Fig. 3. Fertile frond, lax form, from same locality. 
Fig. 4. Fertile frond, compact form, from same locality. 
Fg. 5. Sporangia or capsules, magnified, showing thesmall apical aperture. 
Fig. 6. The same, viewed more obliquely. 
Sphenopteris microcarpa, Lesq. 
Fig. 7, Portion of barren frond, from near Dollar, collected by Mr. A. E. 
Grant. 
Fig. 8. Pinnule, enlarged. 
Fig. 9. Portion of fertile frond, from near Dysart. 
Fig. 10, Pinuule of fig. 9, enlarged, showing sporangia arranged in groups 
of three. 
Fig. 11. Another pinnule, enlarged, more sparsely fruited. 
fig. 12. Two sporangia, magnified, showing slight indication of a mar- 
ginal border. 
Fig. 13, Sporangium, magnified, showing a slight obliquity of the ar- 
rangement of cells forming the marginal border. 
Fig. 14, Another sporangium, magnified. 
Note.—In fig. 7 the engraver has missed the character of the plant. 
The ultimate pinnules are represented as merged together, but should be 
distinctly separate, as shown in the enlarged figure (8). 
Ill.—On certain Limpets and Chitons from the Deep 
Waters off the Eastern Coast of the United States. By W. 
Ee PALL. 
I HAVE received from Prof. Verrill certain limpets or patelli- 
form shells and chitons collected under his supervision off 
the south-east coast of New England, in deep water, by the 
United-States Fish-Commission parties in 1881, with his kind 
permission to describe them. Though without particular 
beauty and of small size, the hope that these specimens would 
prove of interest has not been disappointed. 
Limpets are generally shore or shallow-water mollusks ; 
* Stur, in his ‘Culm Flora,’ describes a fossil fern (Todea Lnpoldi), 
which appears to be similar to Sphenopteris bifida, L. & H. As its fruit 
is unknown, his reason for placing it in the genus Todea seems simply to 
rest on the segmentation of the frond being somewhat of the same nature 
as that seen in such species as Todea superba. 
+ From the ‘Proceedings of the United-States National Museum,’ 
April 24, 1882, p. 400. 
