600 TRANS. ST.. LOUIS ACAD. SCIENCE. 



per Silurian (Lower Helderberg probably) system, on the bank 

 of the RistigOLiche river, at Dalhousie, New Brunswick. 



CCENOSTOMA BOTRYOIDEUM, nOV. Sp. 

 Plate 6. Fig. 13, general view: 13a, section of surface, nat. size; 13^-, vert. sec. enlarged. 



These fossils form hemispherical masses of considerable size. 

 In some places the bed-rock is almost entirely com^Dosed of masses 

 of these species, together with C. constellatum^ varying in size 

 from a few centimetres to a few decimetres in diameter, irregu- 

 larly thrown together. This species is composed of concentric 

 laminfe arranged in a botryoidal manner. These hemispherical 

 undulations do not often exceed two (or rarely three) centimetres 

 in diameter. The surfaces of the laminae are smooth, without any 

 papillae, and the laminte themselves when broken can be removed 

 like the coats of an onion. Sometimes these botryoidal masses so 

 undulate that upon the different individuals there is a graceful 

 depression resembling the osculum of the sponge, Oculo-copina; 

 but this depression does not communicate with the interior of the 

 laminje. The laminae are very thin, and, with the interlaminar 

 spaces, about three pair occur in the thickness of a millemetre. 

 These are connected by pillars, leaving nearly square spaces or 

 cells. In the specimens obtained, the fossils are so mineralized 

 that the spaces have been filled, and subsequently the original 

 calcareous laminEe and pillars have been removed, leaving what, 

 in the fossil, forms the cells. These cells (generally filled), which 

 originally were the pores, extend through the laminte and crowd 

 the surface with minute circular pores. Besides these pores, we 

 find that the mass is traversed by the divergent tubuli character- 

 istic of this genus. These are less than half a millimetre in diam- 

 eter and open on the smooth surface, where they are indicated by 

 apertures on the summit, or on the sides of the mammillated nod- 

 ules, deposited irregularly at from four to eight millimetres apart. 



This species does not appear to bear any structural relation to 

 5". osteolata (of Nicholson), belonging to the Guelph group, al- 

 though it is mammillated somewhat similarly, and in a horizon 

 not very much below those beds. It maybe remarked that in a 

 hemispherical nodule of two centimetres diameter the height is 

 rather more than half that distance. Differing from that Guelph 

 species, the laminae appear to be arranged around imaginary cen- 



