M. K. A. Zittel on Fossil Monactinellidce. 305 
or Cretaceous deposits, which Ehrenberg has figured and 
named in his 1 Mikrogeologie,’ many were probably derived 
from Monactinellidse; but it is rarely that these spongoliths 
possess so characteristic a form that they could be determined 
with certainty when isolated. 
Among the few uniaxial siliceous structures of unmista¬ 
kable habit are the grapnels and mattocks from the Upper 
Cretaceous of Vordorf, figured by me under the name of 
Esperites Carteri *, which agree precisely with those oc¬ 
curring in living Esperice. 
Carter t refers to the Renierin® a circular, cushion-shaped, 
discoidally compressed sponge ( Pulvillus ), consisting of large 
bacillar spicules, from the Carboniferous Limestone of Scot¬ 
land. 
A second genus ( Rhapidkistia , ibid. p. 140), seated like a 
crust upon Hydractinice , from the same formation, is most 
nearly allied, according to Carter, to the existing genus 
Hymerhaphia , which, according to Schmidt’s classification, 
should be referred to the Chalinopsinidte. 
The most favourable state of preservation among the fossil 
Monactinellkke is presented by certain Suberitidse, of which 
coherent skeletons sometimes occur. Of these I know three 
fossil genera. 
Opetionella, Zitt. 
Sponge nodose or bark-like, of irregular form; oscula, 
pores, or canal-system not preserved ; skeleton consisting of 
a layer, about 12 millims. thick, composed of parallel bacillar 
spicules closely pressed together. The spicules are -5-10 
millims. long, awl-shaped, acutely pointed at both ends, 
thickest in the middle. 
I have not observed in the specimens before me any special 
cortical layer with smaller bacillar spicules, or stellate or 
spherical bodies ; possibly they have been washed away, 
possibly they were never present. Notwithstanding their 
absence I place the genus Opetionella in the neighbourhood 
of Donatia ( Tethya ) lyncurium , Nardo, as the spicules of the 
two genera show not only the same form, but also the same 
arrangement. Carter’s Trachya (Ann. & Mag. Nat. Hist, 
ser. 4, vol. vi. (1870) p. 178, pi. xiii. figs. 11-16) must be 
still more nearly allied. In this Suberitic genus the whole 
sponge-body likewise consists only of bacillar spicules of two 
sizes and forms, and a cortical layer is also wanting. Tra- 
* “ Ueber Cceloptychium Abhandl. der k. barer. Akad. der Wiss. II. 
Classe, JBd. xii. pi. iv. figs. 27-29. 
t Ann. & Mag. Nat. Hist. ser. 5, vol. i. (1878) p. 137. 
