80 THE NAUTILUS. 



Fischer, but differs in the wide posterior end and the distinct rays. 

 U. soledadensis was omitted by Simpson, evidently inadvertently. 

 It should go in the Synopsis next to U. popei." 



Unio sp. Valles river. The most plentiful Vnw found. Dall 

 referred it to soledadensis. Pilsbry says " A new species, related to 

 popei, yet with some features of U. medetlimis." 



CYRENID^E. 



Cyrena carolinensis Bosc. Panuco river, Tampico ; found but few. 



Cyrena germana Prime. Panuco river, Tampico. A single ex- 

 ample, more compressed, and lighter colored, but possibly intergrades 

 with carolinensis. 



Pisidium singleyi Sterki. Valles river ; Valles and drift of 

 Panuco river, Tampico. 



Eupera singleyi Pils. Valles river, Valles ; and Tamesi river, 

 Tampico. 



MACTRID^E. 



Mulinia lateralis Say. Panuco river. 



PELSENEER'S TREATISE ON MOLLUSC A. 



A TREATISE ON ZOOLOGY, edited by E. Ray Lankester, PART 

 V, MOLLUSCA, by Paul Pelseneer, London, 1906. This admirable 

 book, of 355 pages, should be studied by every conchologist, although 

 it is not quite elementary, and some fundamental knowledge of 

 zoology is required to fully understand it. The text is well illus- 

 trated by 301 figures, partly diagrammatic, many of them from Prof. 

 Lankester's article " Mollusca " in the ninth edition of the Encyclo- 

 pedia Britannica, 1883. It is interesting to note the considerable 

 changes of classification from Lankester's article to the present book. 

 The editor of the NAUTILUS may permit to cite the main groups 

 here, side by side : 



LANKESTER, 1883. 



Branch A. Glossophora. 

 Class 1. Gastropoda. 



Br. a. Isopleura. 



Br. b. Anisopleura. 

 Class 2. Scaphopoda. 

 Class 3. Cephalopoda. 



Br. a. Pteropoda. 



Br. b. Siphonopoda. 

 Branch B. Lipocephala. 

 Class 1. Lamellibranchia. 



PELSENEER, 1906. 



Grade A. Isopleura. 



Class I. Amphineura. 

 Grade B. Prorhipidoglossomorpba. 



Class I. Gastropoda. 



Class II. kScapbopoda. 



Class III. Lamellibranchia. 

 Grade C. Siphonopoda. 



Class I. Cephalopoda. 



