464 Dr. II. A. Nicholson and Mr. R. Etlxcridge on 



fonn calcareous vesicles, which vary in length from a third of 

 a line to more than half a line, and which have their walls 

 perforated by numerous circular microscopic foramina, cover- 

 ing the whole surface, and placed about their own diameter, 

 or rather more, apart. The cells are produced by budding 

 from one another directly, and are connected by short, con- 

 tracted, tubular stolons in such a manner as to form an open 

 network. 



Obs. A. fusiforme is readily distinguished from A. stella- 

 tum by the fact that the vesicles are directly connected with 

 one another, that they are not arranged in clusters, and that 

 the pores are, on the whole, of larger size, and show no traces 

 of a linear arrangement, whilst the vesicles themselves are also 

 of larger size. The absence of a clustered arrangement and 

 of a network of connecting filaments equally separate this 

 species from A. radians, with the additional distinction that 

 the pores are distributed over the whole surface instead of 

 being confined to a single median row on each vesicle. When 

 the vesicles of A. fiisiforme are fractured, they are seen to 

 contain a large central cavity ; but there are no traces of any 

 other opening in each except the numerous minute pores. 

 These pores sometimes exhibit the appearance of being ele- 

 vated above the general surface ; but it is difficult to say how 

 far this appearance may not be deceptive. Owing also to the 

 adherent habit of this and the other members of the genus, 

 and the small size of the vesicles, we have been unable to 

 examine specimens by the method of transparent sections, and 

 can therefore offer no observations on the minute structure 

 of the chamber-wall. 



Form, and Loc. Hamilton formation (Middle Devonian), 

 Widder, township of Bosanquet, Ontario. Rare, and adlierent 

 on Spirifera mucronata, Conrad. 



Collected by, and in the cabinet of, Prof. Nicholson. 



Ascodictyon stellatum, Nich. and Eth., Jun. 

 (PI. XIX. figs. 1-6.) 



Spec. char. Colony composed of ovoid or pyriform calca- 

 reous vesicles, varying in length from one fifth to one third 

 of a line, and usually disposed in stellate clusters, each con- 

 taining from three to six cells, or sometimes more. The 

 Avails of the vesicles are perforated by microscopic foramina, 

 usually showing a distinctly linear arrangement. The clus- 

 ters are connected together by creeping filamentous tubes, the 

 free surfaces of which are perforated by a single row of minute 

 foramina, and which generally anastomose so as to form a 

 network. 



