58 THE PALEONTOLOGY OF MINNESOTA. 
(Receptaculites owenl. 
the outer side of the vertical rays of the spicules they are not septa]. The distance 
of the cells [circular perforations of the matrix once occupied by the vertical rays of 
the spicules] from each other is variable, those near the center being closer together, 
though, in receding from the center, there are at intervals intercalated rows of cells, 
which take the same direction, and give the cells a closer arrangement towards the 
margin than in the intermediate space before the intercalation of the additional 
rows. The apertures {impression of head-plates] both above and below are essen- 
tially rhomboidal [from 3 to 5 mm. in width|; but in well preserved surfaces there 
are remains of rays, which, however, are rarely observed ; and I have not seen them 
on opposite sides of the same specimen.” 
A small specimen of this species from Goodhue county, Minnesota, has the lower 
surface preserved as crystalline calcite, while all other portions of the sponge are 
missing. The outline of the plates cannot be determined, but their arrangement is 
well indicated by a series of knobs arranged in quincunx. These were regarded at 
first as having been produced by the wearing away of the softer matrix surrounding 
the crystalline calcite, usually filling the interior of the vertical rays of the spicules 
in Minnesota specimens. Upon grinding the specimen transversely to the surface, 
it was discovered that the vertical rays of the spicules are not present, and that only 
the lower or outer surface of the sponge is preserved. We therefore conclude 
that each head-plate in this specimen had originally a central knob similar to those 
figured by Dr. Hinde in Sphwrospongia tessellata Phillips, sp.* In the latter these 
knobs are comparatively smaller than in Receptaculites oweni Hall. 
The upper or inner layer is never preserved entirely in Minnesota specimens of 
R. oweni, and we shall therefore give Dr. Hinde’s description of this integument as it 
occurs in R. occidentalis Salter, a closely related species: “The vertical rays in this 
species of Receptaculites continue cylindrical to near their basal extremities, and then 
abruptly expand into horizontal plates. These plates have four straight sides, but 
at each of the corners there is a semicircular or semi-elliptical vertical hollow.+ 
Each plate appears also to be traversed by four horizontal canals, which radiate 
from the center, where they_are in connection with the canal of the vertical ray. 
* * * These plates are intimately united together so as to form a continuous 
inner or upper layer. The delimitations of the separate plates in this layer are not 
always preserved ; in many specimens they appear to have been completely oblit- 
erated, and the layer resembles a continuous plate with numerous cylindrical or 
elliptical canals which penetrate through it at right angles” (/oc. cet. p. $25). In 
many specimens from Minnesota, the horizontal canals of the upper or inner layer 
*Loc. cit. pl. 37, fig. 1b. : * 
+Herr Raut? states, that these vertical hollows or pores did not originally exist in the “ gastral” wall, but are the result 
of fossilization (Nicholson “* Manual of Palzontology, vol. ii, p. 1564). 
