HE present volume is devoted to the monographs of Tecti- 
branchiate mollusks, in continuation of Volume XV. The 
CEPHALASPIDEA herein monographed belong to groups of 
which but few species are represented in the collection studied, so 
that little beyond the merits of a careful compilation can be ex- 
pected. In the ANAsPIDEA, more material has been available, and 
it is hoped that progress has been made in the classification and defi- 
nition of subfamilies and genera, as well as in the facilitation of 
specific determinations. To a less extent this also applies to the 
NorasPIDEA. 
A single family of AscoGLossa, Oxynoeide, is included herein, on 
account of the Bulla-like shell developed. The other AscoGLossa 
and the NuDIBRANCHIATA proper, which have no shells when adult, 
will not be included; the fruitful labors of Bergh rendering their 
treatment here inadvisable, especially in view of the fact that few 
conchologists concern themselves with those groups. 
In an appendix, the Tectibranch groups of Volume XV are 
brought up to 1896. 
A brief introductory chapter embodies the views of the author on 
the classification of CrEPHALASPIDEA; the chief departures from 
previous arrangements being in the dismemberment of the old family 
Bullide, with the creation of Akeratide ; and the rearrangement of 
the families into phyla based largely upon the mode of specialization 
of the radula, and the development of the pleuropodial lobes. 
1S Laws Wd 
ill 
