— 39 — 
the peristome and a more complete and regular separation of its parts. 
The number of the teeth, so variable in the Buxbaumiaceae and also in 
the Polytrichaceae is already reduced to sixteen in our Encalypta , but each 
of these yet contains several layers of cells in thickness and several rows in 
width.” The gradual reduction to the normal type takes place almost 
before our eyes in the genus Encalypta. There are forms of E. longicolla 
in which there are but three filaments on the face of each tooth, and there is 
often only a single layer of internal cell cavities. The reduction becomes 
even more apparent in the closely related E. brevicolla. 
In E. apophysata the peristome is composed of sixteen long and narrow 
teeth conni vent in the form of a cone. Upon the dorsal face of each of these 
teeth are two rows of reddish or orange plates separated by a median line 
along which the tooth is sometimes perforate. In thickness there are ordi- 
narily three layers, two in contact with each other and a third inside these 
and separated from them by narrow elongated cell cavities. This layer 
rarely extends the whole length of the teeth and may be present near the 
base only. It is easy to recognize on the one hand the homologies of this 
peristome with that of E. longicolla and on the other with the normal Arthro- 
dont peristome. The two outer layers of united plates correspond to the two 
layers of plates in the teeth and the third corresponds to ttie inner peristome. 
In E. procera (Plate IV. Fig. 12,) there is an external peristome of sixteen 
narrowly linear, much elongated teeth, but which in number and arrange- 
ment of plates is typical of the Arthrodont-Diplolepid external peri- 
stome, i. e., two rows of outer plates and one of inner plates. Directly inside 
these outer teeth are sixteen inner teeth. These inner teeth are a little 
shorter than the outer and are formed of an outer papillose layer of plates 
and an inner more strongly thickened layer. These inner teeth are united 
below into a basal membrane about one-fourth the entire height of the inner 
peristome ; this membrane is also united to the outer teeth by unabsorbed 
radial walls as in E. apophysata. Alternating with the teeth are sixteen 
narrow processes which Philibert states to be homologous with the keels of 
the inner peristome of the Diplolepideae. 
Comparing this peristome of E. procera with the typical peristome of 
the Diplolepideae as illustrated and explained in previous articles there will 
be little difficulty in recognizing the corresponding and homologous parts. 
In the later development in Mnium and Hypnum the reduction in the num- 
ber of elements in the teeth has been followed by a great increase in the 
breadth of the remaining elements. 
AN INTERESTING MOSS BOOK. 
A. J. Grout. 
Mr. Wm. L. Sherwood, President of the New York Naturalists’ Club, has 
in his library a copy of “Twenty Lessons on British Mosses,” by Wm. 
Gardener, of Dundee, published by Longman, Brown, Green & Longmans, 
London, in 1847. It is an exceedingly interesting little volume and apparently 
rare as I have never before seen a copy, and do not remember ever having 
heard of the book. 
