This, however, is not generally retained in one plane, and the spire projects, little by little, on the side which was originally left, but finally becomes right (in dextral forms, with a clockwise direction, if viewed from the side of the spire; but counter-clockwise in sinistral forms).
In dextral Gastropods the only structure found on the topographically right side of the rectum is the genital duct.
Burr.- p T 9 pl.y ped.g: reversal of the cleavage planes in sinistral as compared with dextral forms. The facts, however, strongly suggest that the original cause of the torsion was the weight of the exogastric shell and visceral hump, which in an animal creeping on its ventral surface necessarily fell over to one side.
Shell bulimoid, dextral or sinistral; radular teeth, expanded at their extremities and multicuspidate.
In a dextral Gastropod the shell is coiled in a right-handed spiral from apex to mouth, and the spiral also projects to the right of the median plane of the animal.
Lanceolatus obtained by the tow-net in 8 -10 fathoms, showing the asymmetry of the large lateral sinistral mouth with its ciliated margin cm and the dextral series of simple primary gill-slits (Ips-14ps).