ART. 4 CAMBRIAN CONCHOSTRACA — ULRICH AND BASSLER 51 



A. bergeroni, are greatly like Lepiditta, the principal, or rather most 

 striking difference being the antero-ventral node wliich is wanting in 

 the latter genus. The dorsal depression which is usually present in 

 Aluta likewise is absent in that genus. A. rotundata suggests very 

 different affinities, namely with Beyr-ichona. In fact, in the lobation 

 of the valves this species is so highly suggestive of that genus that 

 the resemblance is believed to be indicative of true genetic relation- 

 ship. Further, if the hinge of A. rotundata were longer, the post- 

 cardinal angle narrower, and the outline less oblique, this species 

 would probably have been referred to Beyrichona, as has already been 

 suggested by Matthew, ^ rather than Aluta. Finally, most of the 

 species of Aluta recall the much larger forms comprised in the genus 

 Dielymella. That genus is, of course, distinguished readily enough 

 by its gaping valves and its evenly convex surface contours, there 

 being no sign of either the antero-ventral node or the dorsal depression 

 generally found in Aluta. Still, when the latter is absent, as in A. 

 troyensis, it is difficult to escape the conviction that some genetic 

 relation exists between the two genera. Two of the species, A. 

 troyensis and A, rotundata, were referred by Walcott ^ to Aristozoe. 

 While presenting a general resemblance to that remarkable Silurian 

 genus of Phyllocarida, or of Phyllopoda, there should be little doubt 

 that these Cambrian bivalved crustaceans belong to a very distinct 

 genus. Compared with Aristozoe, these differ not only in being much 

 smaller but in the more important fact that their valves close tightly 

 all around instead of being curved so as to gap widely at the ends. 

 Compared further they are found to differ in the general outline of the 

 valves, in having a dorsal depression, and in the more antero-ventral 

 position of the node or nodes. Finally the shell differs in being 

 thinner, more flexible, and less calcareous in composition. In the 

 position of the nodes Aluta is like Callizoe, another Silurian genus 

 described by Barrande; but as that genus is generally regarded as 

 related to Aristozoe, there is probably no direct alHance between it 

 and Aluta. 



Viewed as a genus, Aluta can not very well be classified except as 

 an aberrant member of the family Beyrichonidae. The type differs 

 from Polyphyma, Beyrichona, and Hipponicharion, the three other 

 more typical members of the family, in the comparative brevity of its 

 hinge and particularly in the reduction of the postdorsal angle. 

 The latter feature is responsible for the prevailing obliquity of its 

 outline, in which respect Aluta agrees with some of the Bradoriidae. 



8 Trans. New York Acad. Sci., vol. 14, 1S95, p. 133. 



* Amer. Journ. Sci., ser. 3, vol. 34, 1887, p. 193; 10th Ann. Rep. U. S. Qeol. Surv., 1890, p. 62 8. 



