INCISURA (scissueella) lytteltonensis. H 



gland is much the smaller of the two (figs, 7 and 8) ; posteriorly 

 it is a narrow strip of glandular epithelium lying between the 

 terminal part of the rectum ; anteriorly in front of the anus 

 it becomes broader and extends about as far forward as the 

 level of the mantle slit, but stops far short of the anterior 

 border of the mantle. In this pre-anal region the right and 

 left hypobranchial glands are very closely approximated in 

 the middle line. The right hypobranchial gland has approxi- 

 mately the same anterior extension as the left, but runs back- 

 wards on the right side of the rectum nearly to the posterior 

 end of the mantle-cavity. Comparing the arrangement with 

 that described by Woodward for Pleurotomaria, it is obvious 

 that the pre-anal portions of the two glands of Incisura 

 correspond to the large anterior hypobranchial gland, " par- 

 tially divided by a median longitudinal furrow into two 

 halves," of Plenrotoniaria, and the posterior portions of the 

 two glands of Incisura correspond to the two "additional 

 mucous glands " lying on either side of the rectum of Pleuro- 

 tomaria. But whereas in the latter genus the left additional 

 gland is conspicuously the larger, in Incisura it is the right 

 posterior portion of the gland which preponderates in size, 

 the left gland being small, no doubt because of the relatively 

 large size of the left kidney, for the hypobranchial gland 

 does not extend beneath this organ. 



The pericardium, as in all Rhipidoglossa except the Helici- 

 nidas, is traversed by the rectum. It is relatively of large 

 size, and can always be distinguished in whole specimens as 

 a clear space surrounding the first bend of the rectum on the 

 left side of the body behind the columellar muscle. At this 

 point it lies close to the surface of the body, and its outer 

 wall is very thin and transparent (tig. 11). The exact limits 

 of its extension to the right are very hard to make out, 

 because the left kidney projects into it from above, and its 

 cavity is largely blocked by the auricles. Its extent, as far 

 as I am able to determine it by reconstruction from sections, 

 is represented by the thick black line in fig. 4. The large 

 transverse extension of the pericardial space, as compared 



