«'130 The Ottawa Naturalist. [Jan, 



A study of this plate with a stereoscope seems to show that 

 the denticles were arranged in double pairs, i. e., with four 

 denticles arising from each node. In the lowest group there 

 seems to be a denticle occupying a middle position between 

 the pair at the sides, l)ut its apertural margin and parts of its 

 ventral stirface are lost. In the next group above, the gum 

 mounting allows us to look deeply within the branch and see 

 (£rom the inside) the ventricose portion of a denticle on the 

 distant side of the axis. Above this opening there remains a 

 portion of a denticle facing the observer. The next group 

 above also shows portions of a third denticle. The fourth or 

 topmost group has been cut across diagonally by weathering. 

 The openings on this surface present additional evidence that 

 each node bore, at least, four denticles. . 



The plate shows clearly the value of mounting with gum 

 damar, for such mounting not only served to render the surface 

 more transparent and increase the contrast between the black 

 remains of the chitin and the inatrix, btit it also aided in securing 

 that sharpness of outline which still appears in the subsequent 

 enlargement to 60 diameters. 



The specimen is named in honor of Dr. Rudolf Ruedemann, 

 to whom the writer, and the world as well, is deeply indebted 

 for his work on this interesting group of fossil organisms. 



The detail of Urasterella pulchclla, Bill., which is repro- 

 duced on this plate, shows some of the flooring ossicles (am- 

 bulacra) of the arm, anuml^er of arm marginals wnth spine bases, 

 and an apparently double interradial marginal. The ambu- 

 lacral plates, here lost, are elsewhere present and functioned as 

 true covering plates. That is they could be closed so as to meet 

 each other over the food groove or they could be held in a 

 widelv open condition and the five interradial pairs could 

 fimction as jaws. More complete details of this species will be 

 given in another article. 



THE BANDED POCKET MOUSE, PEROGXATHUS 



FASCIATUS WIED. 



By Stuart Criddle, Treesbank, Man. 



The mouse forming the title of this paper was discovered 

 and described by Maximilian, Prince of Wied, in 1839. It was 

 collected on the upper Missouri river near the mouth of the 

 Yellowstone, North Dakota , and proved to be a new genus as 

 well as a new species. It w^as, also, the first pocket mouse to be 

 found in North America. Since the original discovery of pocket 

 mice on this continent, however, the ntmiber of known species 



