348 The American Geologist. May, 1 897 
has been amended so as to include A. bellistirata Hall, the type A. 
amygdaUna Hall, and a new species A. afflnis, whilst the genera Cli- 
onychiu (Ulrich), and Byssonychia are made to include the remainder of 
the known species of the Ambouychiidfe of Minnesota, and for that mat- 
ter of other portions of North America. . One new species each of Cli- 
onychiii and Byssonychia are described: C. nitida and B. tenuistriata. 
[The genus Whiteavesia has been created, p. 513 et seq., for the re- 
ception of certain forms of ModiolopaiH such as M. cincinnatiensis Hail 
and Whitfield; M. modioUformis M. and W. To these two forms Ulrich 
adds another, Whiteavesia, W. Hubearinata]. 
The genus Orthodesma has not been disturbed but certain spe- 
cies "of the same general type as Modiolopfiis and Modiinorplta,'''' 
having from one to //Vree oblique cardinal teeth in each valve, have found 
a resting place in the newly-constituted genus 3Iodiolodoii, with M. ovi- 
formis Ulrich (sp.) as the type, M. uiincJieUi, M. ganti, M. X)aUdun 
and M. ? gibbus, most of which Ulrich states might have been placed 
in his own genus IscJiyrodonta. 
Colpomya is a new genus made to receive four forms: M. constricta, 
the type from Kentucky, M. demissa (a Minnesota species) and two 
other species. Modiolopsis milleri Ulrich, and ilf. /a&a Hall are also 
placed under this general description. 
AristereUa nitidulu Ulrich, is a newly described form both as to 
generic and specific name. Ulrich says of this species: ''It might have 
been placed into either Actinomya or Euryinya, were it not for its un- 
equal valves." 
Certain forms previously referred to the broad genv\& Modiolopsis have 
been referred to Endodesma, E. cunetum Ulrich, being the type. Six- 
species are referred to this genus. Ulrich doubtfully placed them "near 
Rhytiniya Ulrich, an early type of the Pholadellid^." Modiolopsis 
trentoiiensis is also referred to this genus. 
Psiloconcha, a genus very closely related to Modiolopsis or Orthodesma 
has been created to i-eceive P. grandis Ulrich, P. minnesotensis and a 
number of other forms from other states. Prolobella is also doubtfully 
referred to the Modiolopsidce, P. striatida Ulrich being made the type, 
whilst Avicida trentoneusis and ^4. ovifortnis of Hall, 18i7, are also re- 
ferred to this new genus. 
In the Cyrtodontidae of Minnesota Ulrich includes: Cyrtodonta Bil- 
lings, Vanuxemia Bill., Matheria Bill., and his own genus Whitella. 
Cyrtodonta rugosa andC canadensis, both of Billings, are taken as the 
types of this genus. Ulrich adopts Cyrtodonta of Billings instead of 
Conrad's genus Cypricardites, and on page 535 gives his reasons in a 
clear and concise manner. Cyrtodonta is used both by Canadian and 
European authors, and we agree with Mr. Ulrich in his remarks, except- 
ing his last remark regarding the use of the term Cypricardites in no- 
menclature. We think it very unwise to refer any form of fossil organ- 
ism to a genus which has not positive status in the department of 
palaeontology. 
