A crude cellulase extract was prepared from the hepatopancreas of a marine mollusc, Dolabella sp., and partially purified by ammonium sulphate fractionation. 2. The optimum pH values of the partially purified preparation were 6.5 and 8.0 for Walseth cellulose and CM-cellulose respectively. It was most stable at pH6.0 and showed moderate thermostability. 3. The partially purified preparation was subjected to starch-zone electrophoresis, and incompletely resolved into several fractions that contained one or more cellulase components of different substrate specificity. 4. Some of these cellulase fractions showed practically no aryl beta-glucosidase activity and hydrolysed aryl beta-cellobioside with difficulty. From substrates such as higher cello-oligosaccharides, cellodextrin, CM-cellulose, Walseth cellulose and cotton fibre, they produced cellobiose as the major and cellotriose as the minor end products, both of which were resistant to further attack by cellulase. 5. From the slope of the curves of viscosity-reducing power for CM-cellulose, the cellulase components from Dolabella were presumed to be of a ;more-random' or a ;less-random' type in the mode of action. 6. In the hepatopancreas of this mollusc, beta-glucosidases were also present, which hydrolysed cellobiose as well as aryl beta-glucosides. The optimum pH values of these enzymes were about 5.5.
