THE NAUTILUS. 39 



These facts, however, do not affect the general question. It is 

 quite evident that a systematic arrangement of the marsupia does not 

 coincide with a natural system of the family. The species of Diplo- 

 don of New Zealand, which I have examined, had filled only the 

 inner gills with eggs ; but Suter has observed that sometimes eggs 

 are also found in the outer gills. Simpson says that in the species of 

 Quadrula, both the gills are filled with eggs, but that sometimes the 

 inner gill contains but few. We cannot doubt that in the most an- 

 cient Unionidce the eggs were discharged only into the inner gills and 

 that later all four gills were filled with eggs, representing the last 

 stage, the exclusive employment of the outer gills. In the genus 

 Qtiadrida all these successive stages are still represented ; and it is 

 not admissible to use such differences for the establishment of genera. 

 It happens that in the same species are observed great differences in 

 this respect. The specimen of Qaadrida heros Say, examined by Lea, 

 had filled with eggs all the four gills ; while the specimen examined 

 by Sterki had only the hinder part of the outer gills filled with eggs, 

 as in many species of Lampsilis. According to the classification of 

 Simpson, which in this respect is an artificial one, these specimens 

 would fall in quite different genera. Differences of this nature have 

 caused Simpson to separate from Quadrida various species and 

 sub-genera. It is no natural disposition when we see Pleurobema 

 allied with Unio, Quadrula tuberculata Bar. widely separated from 

 the nearly related species speciosa, forsheyi, etc.; Obliquaria reftexa 

 widely remote from Quadrida metanevra; Quadrida cesopus allied to 

 Pleurobema. In the same manner is Lampsilis phaseolus separated 

 from L. iris, etc., because the development of the marsupium is more 

 extensive. Therefore it is necessary to associate these separated 

 groups with their real relatives. 



[To be concluded.') 



A NEW COLOMBIAN CLATJSILIA. 



BY HENRY A. PILSBRY. 



Nenia Smithies, n. sp. PI. II, figs. 10, 11, 12. 



Shell cylindric-fusiform, rather thin, lusterless, nearly smooth, 

 obsoletely marked with growth-wrinkles ; of a rich purplish-brown 

 color. Whorls 8-|, moderately convex, the penultimate widest, those 



