a new Genus of Palceozoic Fossils. 465 



Ohs. In its youngest stage (PL XIX. fig. 6), A. stellatum 

 presents itself simply in the form of scattered oviform or pyri- 

 form calcareous vesicles attached to the exterior of foreign 

 bodies. When mature, it consists of similar vesicles com- 

 bined into clusters, generally of three to six in each, these 

 being connected by ramifying and anastomosing tubular 

 stolons (PI. XIX. fig. 1). The new vesicles are produced 

 from the sides of the stolons, or are budded forth in rosettes 

 from the nodal points where the stolons intersect one another. 

 The rosettes may be comparatively remote ; in other in- 

 stances they become so aggregated together as almost to con- 

 stitute a continuous crust. The walls of the vesicles are 

 perforated by minute apertures (PI. XIX. fig. 2), which are 

 generally arranged in lines, and are not so numerous as in 

 A./usiforme^ whilst they can only with difficulty be detected 

 in specimens infiltrated with carbonate of lime. The vesicles 

 are seen, on fracture (fig. 5), to be hollow ; and they may 

 coalesce in the centre of each rosette, or there may be a central 

 chamber, the nature of which we have been unable to deter- 

 mine. The connecting tubes or stolons are also undoubtedly 

 hollow ; and they carry a single row of pores (fig. 3) on their 

 free surfaces, though these openings can only be detected in 

 well-preserved specimens. The stolons may arise from one 

 another, from the central points of the rosettes, or occasionally 

 by direct prolongation from the distal extremity of a vesicle 

 (PI. XIX. fig. 4). 



In the fact that the vesicles are, typically, disposed in 

 rosettes, and are connected together by a creeping network of 

 tubes, A. stellatum resembles A. radians. It is, however, 

 readily distinguished from the latter species by the ovoid or 

 pyriform shape of the vesicles, and the fact that there is 

 always more than a single row of pores to each vesicle. 



Form, and Loc. Not very rare in the Hamilton formation 

 (Middle Devonian) of Widder, township of Bosanquet, Onta- 

 rio. Parasitic on Spirifera mucronata, Conrad, and Cyrtina 

 hamiltonensis, Hall. 



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



Ascodictyon radians ^ Nich. and Eth., Jun. 

 (PI. XIX. figs. 9-11.) 

 Spec. char. Colony composed of elongated vesicles, broad 

 at their bases, thickened out in the middle of their length, 

 and gradually attenuated towards their extremities, disposed 

 in stellate clusters or rosettes. The bases of the tongue-like 

 or somewhat fusiform vesicles are placed round a central cir- 

 cular depression ; and their lengtli varies from a sixth to more 



