165 



on to the pin's head, so that the plane of aperture is parallel to the 

 length of the pin, and the axis of the shell at right angles \vith it. 

 In this positiou the operculum, if there, or if not, the inside of the 

 aperture, and also tlie apex and umbilicus, and indced all parts of 

 the shellj except the point of attachment, can be brought under the 

 niicroscope by revolving the pin. 



Next, let me explaiu any new terms I may have used. In speak- 

 ing of "above " or " below," I always consider the apex the upper- 

 most, and the umbilicus the lowermost part. In speaking of " right " 

 or " left," the outer edge of the aperture is cousidered to be ou the 

 right hand. 



In pursuing the examination, we gire in succession Form and Co- 

 lour. Those two are manifest. Sculpture : we commence to describe 

 the sculpture of the lašt whor], and calculate from below the suture 

 downwards towards the umbilical region at about a ąuarter from the 

 aperture, or the lašt quarter or third of the lašt whorl. Sjnral 

 carince are sculptured raised lines, transverse to the axis or column 

 of a shell. The spire and its outliues are self-evident. TVhorls are 

 counted from the aperture upwards ; from that part to vvhere it is 

 opposite or attached to, what is termed, the body whorl, form s one 

 whorl, and so on upwards, the whole, half, third, or ąuarter being 

 determined by the exact termination of the appearance of a suture 

 at the nuclear apex. The aperture, or mouth, though not audibly, 

 speaks its own shape, &c. Labrum in Stoastoma is the edge of the 

 right-haud portion of the aperture, extending from the suture, as it 

 were, above, round on the right, till it finishes its curve below ; the 

 labium being the almost straight part on the left. Labral and labial, 

 coined words, refer to those parts of the edge of the aperture, &c. 

 Labrum " double " denotes a more or less fine, sharp groove close 

 behind the very verge of the labral side of the aperture ; and it shows 

 that some at least of StoastomidcB have peristome and peritreme, 

 though never prominent or expanded as in Choanopoma fimhriatulum, 

 C Chittyi, and the ILke. 



The ^'labral lamella" is a term we adopt, equivalent to ^Idams's 

 " spirai lamella," " lamellar spirai keel," " spirai carina coutinued 

 into the lower extremity of the labrum," &c. ; or the " lamelliform 

 keel," "basai margin continued," &c., "small lamella," "raised la- 

 mella," &c. of Pfeiffer, Cat. Phan. I call it "labral" lamella, be- 

 cause it appears to me to grow out of the labral side of the shell, 

 one specimen of Lewisia Agassiziana in progress of development 

 clearly denoting the fact. It answers to the " umbilical keel" 

 of some of the Cyclotus. In " measurement " of height the axis 

 is placed at right angles to the base, so that " height " signifies 

 distance between two parallel lines, the apex touching one, and the 

 extreme lower edge of the aperture touching the other, the axis 

 being at right angles. " Greatest breadth " measures from the edge 

 of the aperture about the periphery to its extreme opposite at the 

 other side of the lašt whorl, the axis being still at right angles. 

 "Least breadth" is when three parts of the last whorl touch two 

 parallel lines, that is, the plane or edge of the aperture, the back of 



