. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology. 6 Bulletin Museum of Comparative Zoology, Vol. 150, No. 1 visceral ganglion stonnach anus comb sipho. diverticula add. nnus. oesophagus cerebral ganglion ense n palp proboscis 'byssal' gland mm Figure 2. Spinula filatovae. Semidiagrammatic view of right side of the animal to show disposition of the organs. additional lobe that thinner and nar- rower than the former, but which lies par- allel to it and extends the length of the feeding aperture. The epithelium on the ventral side of the additional lobe, the dor
. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology. 6 Bulletin Museum of Comparative Zoology, Vol. 150, No. 1 visceral ganglion stonnach anus comb sipho. diverticula add. nnus. oesophagus cerebral ganglion ense n palp proboscis 'byssal' gland mm Figure 2. Spinula filatovae. Semidiagrammatic view of right side of the animal to show disposition of the organs. additional lobe that thinner and nar- rower than the former, but which lies par- allel to it and extends the length of the feeding aperture. The epithelium on the ventral side of the additional lobe, the dorsal side of the muscular lobe, and the epithelium between the two, is richly supplied with acidophilic gland cells. This band of gland cells is continued an- teriorly to the inside of the inner mus- cular lobe, although the cells here are fewer in number. Internal to the feeding aperture, there is a series of fine radiating pallial retractor muscles, and it is clear that this area of the mantle is capable of considerable extension. The tips of the contracted palp proboscides lie close to the second mantle lobe. Although there is no fusion ventrally to form a separate aperture, the opposing inner muscular lobes undoubtedly come together at this point and thus separate the feeding ap- erture from the extensive pedal gape. The adductor muscles are unequal in size (Fig. 2), with the 'quick' and 'catch' parts obvious (Fig. 4). The smaller pos- terior adductor muscle is pear-shaped in outline. The anterior adductor is cres- cent-shaped and about times as large in cross section as the posterior. Imme- diately below the anterior adductor, at the mantle edge, is the anterior sense or- gan (see p. 24). A single siphonal tenta- cle, common to many protobranch bi- valves, arises from a short pocket on either the right or left side of the base of the siphon. The tentacle is developed from the middle sensor\' lobe of the man- tle. It consists of an elongate, finely ta- pering cone which
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