"Die Kalkschwamme: eine Monographie; 3 volumes: Berlin, 1872.

H.J.Clark published a paper "On the Spongiae Ciliatae as Infusoria flagellata" in the "Mem.

Boston Nat.
Hist.

Soc." Volume I., Part iii., 1866.

See Hackel, op.cit., Volume I., page 24.) Your book with sixty plates will be magnificent.