Casey — Notes on the Pleurotomidae. 139 
majority of them have the anal sinus situated on a posterior 
declivous or concave fasciolar surface as in Surcula and re- 
lated genera, but, in some instances, as the very isolated 
Glyptotoma, the sinus is medial and formed on a prominent 
periphery. This peculiar group of genera is entirely and long 
since ‘extinct, except Cochlespira, which appears to have a 
history almost as extended as Gremmula from the Eocene to 
the present time, and Aforia, Antiplanes and Megasurcula, 
which as far as known are exclusively living. It is the only 
group containing reversed or sinistral shells, a character which 
seems to be of generic value, as I have never seen a dextral 
specimen of Stnistrella americana Ald., among a very large 
number examined, although otherwise Sinistrella is rather 
closely allied to Trypanotoma, a very distinct genus founded 
by Cossmann upon the Pleurotoma terebriformis of Meyer. 
‘It is also the only group in which the plications of the col- 
umella become in any way a conspicuous feature, although 
this character does occur in some of the Surculid genera in a 
less developed degree; it is greatly developed in Luchetlodon, 
Scobinella and Glyptotoma. In Clinura and Cochlespira the 
whorls are broadly expanded into a thin spiral plate usually 
reflexed and crenulate at the edge. In Aforia circinata Dall, 
this expansion is reduced to a small but abruptly formed 
median ring. 
Eucheilodon Gabb. 
This genus is abundantly distinct from Scodinella in having 
the anal sinus formed upon an elevated and prominent peri- 
pheral shoulder well above the middle of the whorls, and not 
in a concave posterior fasciolar area; it also differs materially 
in the embryo, which, although of the same general multi- 
spiral type, is very much larger, and in the form of the outer 
lip, which does not have the broadly lobed and advanced 
form of Scobinella, in its very narrow linear aperture with 
more strongly lyrate outer lip and in possessing a columella 
fold near the posterior end of the inner lip, which is never 
present in Scobinella. The system of columella folds is 
more elaborate than in that genus and the spiral lyrae are 
