70 Zoological Society : — 



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 Stoastomidce have peristome and peritreme, 

 though never prominent or expanded as in Choanopoma fimbriatuluniy 

 C. Chittyii and the like. 



The '■'■lahral lamella''^ is a term we adopt, equivalent to Adams's 

 "spiral lamella," *' lamellar spiral keel," "spiral carina continued 

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

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

 mella," &c. of Pfeiffer, Cat. Phan. I call it ''lahraV 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 keeV* 

 of some of the Cycloti. 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 last 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 

 the last whorl, and narrowest part of it close to the aperture, or the 

 penultimate whorl. 



With, then, the one species from Polynesia, Electrina succinea, 

 the total of StoastomidcB amount to 8 1 species known ; and I proceed 

 to propose an entirely new arrangement of them. Professor Adams 

 foresaw the necessity and propriety of it. In his * Monograph of 

 Stoastoma,' p. 4, occur the following passages : — " The value of this 

 genus is equal to that of the Lamarckian genera of Cyclostoma and 

 Helicina. If these should be generally received as families, sub- 

 divided into several genera according to the plan of Dr. L. Pfeifi'er, it 

 will be entitled to constitute a distinct family, Stoastomid^. Some 

 of the characters rarely, if ever, occur in other genera, while the 

 specific differences consist partly in slight modifications of these 

 characters. Such are the blunt but not reflected edge of the labrum 

 and the spiral lamella issuing from the umbilicus. The genus has 

 thus a very obvious type, quite distinct from any hitherto discovered. 

 An affinity with the Cyclostomidce is established between Apero- 

 stoma (Troschel) and the depressed and discoidal species of Stoa- 

 stoma.''* " Its affinity with the Helicinidce is established between 

 Lucidella (Swainson) (? ?), and some of the conical species, as S. 

 Redfieldianum and S. Leanum, by their general form and sculpture, 

 and by the form of the base. But observations on the animals will 

 be of more value on this subject. We were not so fortunate as to 

 obtain living specimens. While preparing this Monograph, a cor- 

 respondent informs us that S, pisum when alive is sea-green." 



In raising Stoastoma into a family, I am thus justified by Pro- 

 fessor Adams, and only carry out his views in caUing it, Family 

 Stoastomidce, Adams. 



