2")i> The American Geologist. October, 1894 
Byssonyelda, nov. (type, Ambonychia radiata Rail), possesses ;i byssal 
opening and both cardinal and lateral teeth. 
The genus Modiolopns, Hall, is carefully restricted and itsclose generic 
relation i<> the Devonian Modiomorpha pointed out. 
Hurt/mud, nov., is founded upon Hall's species Modiolopfds plana, and 
is distinguished by its posterior ala and striated ligamental area. 
Actinomya, changed in the errata to Whiteavesia, now (type. ModiohpsU 
cincinnatienm Hall and Whitfield), hears surface radii, is without cardi- 
nal teeth, and has a short ligamental groove on each side ol the beak. 
Modiolodon, nov. (type. Modiolopsis oviformis Vlrich), is similar to Mbdio- 
lopgis, but has cardinal teeth on each valve. 
Colpom/ya, nov. (type, 0. constricta nov.), has the external form of Modi- 
oloptris, but possesses a strong rostral tooth-like process in each valve. 
AristereUa, nov. (type. A. nitidula, nov.). Similar to Actinomya, except 
in its inequal valves. 
Endodesma, nov. (type, E. cuneatum, nov.). These are ventricose but 
edentulous shells with well defined lunule and extremely faint muscular 
scars. 
Pmloconcha, nov. (type, /'. grandie Ulrich), embraces elongate, com- 
pressed shells with edentulous hinge and linear ligamental groove. 
ProlobeUa, nov. (type P. striatula, nov.). The author considers Con- 
rad's AvicuUi trriitnin'uxix a member of this new genus, but this is a 
species which Jackson has placed among the probable members of his 
genus Uliombapteria, the generic radicle of the aviculoids. 
WMtella, Ulrich (type II' obUquata Ulrich); short, ventricose shells 
with prominent urn bones, sharply defined escutcheon, and two to five 
oblique teeth in front of the beaks. 
Plethoeardia, Ulrich (type, P. umbonata Ulrich); tumid shells with en- 
rolled beaks. "A Strong and large process projects forward and down- 
ward from the under side of the hinge beneath the beak of each valve," 
and the shell bears a strong linear lateral tooth. 
Ctenodonta, Salter (a name which the. author adopts .in preference to 
Hall's earlier term Tellinomya), is divided into six groups, designated not 
by subgeneric terms, but by the names of characteristic species. 
Alhdesma, Ulrich (type. Mbdiolopsis subelKptieum Ulrich), is applied to 
small shells with anterior beaks, strong anterior adductor scars mar- 
gined within by an elevated ridge, hinge with cardinal, posterior lateral, 
but no anterior lateral teeth. 
Rhytimya, nov. (type. /,'. producta, nov.). is regarded as, a pholad and 
allied to Pholadella, Cvmitaria and AUorisma. 
Saffordia, nov. (type. S. ventralin, nov.). Small shells Similar to G-ram- 
mynia, with sharph defined lunule and very large external ligament 
grroove. 
The total number of species described is 130, divided as follows: Am- 
bonychia I. CUonychiab, Byssonychia 2, Modiolopm 11, T8urymya\,_Acti- 
nomya {WJiiteavesfa) 2, Orthodesma 4, Modiolodon 2, Colpomya\, Ariater- 
ella 1. Endodeama5, PsUoeoncha 1. ProlobeUa 1, Gyrtodonta 1(>, ^amitemia 
1."). MatJieria 1. WhiteUa 12, Pletkocafcdia 2, Cienvdottta 26, GHdophovus 2, 
