236 Description of new Lower Silurian Sponges .— Ulrich. 
spaces. At other times the striae cross eaeh other diagonally, 
producing appearance not much unlike that of the ordinary 
arrangement of the spicules in the Dictyospongidce. 
Type, R. Mosa , n. sp. 
EXPLANATION. 
Fig. 1. Upper extremity of specimen of Rauffella jilosa Ulrich, of 
the natural size. 
Figs. 2 and 4. Small portions of fig. 1, x 9, showing the irregular 
character of the superficial network. 
Fig. 3. Thin section of Rauffella palmipes Ul., x 35, showing the 
porous character of the inner layer of the sponge. The spicules were 
not determined and no attempt was made to represent them in this 
hasty sketch. 
Fig. 5. Portion of an example of Heterospongia Jcnotti Ul.; of the 
natural size. 
Fig. 6. Transverse section of a calcareous specimen referred with 
doubt to Heterospongia subramosa Ul. nat. size. 
Fig. 7. Example of Saccospongia rudis, Ul.; of the natural size. 
This figure was inverted by the engraver, its upper extremity, where a 
