JUKES-BROWNE : ON CALLISTA, AMIANTIS, AND PITARIA. 347 



with a single groove ; teeth thin and weak ; left posterior cardinal 

 short and marginal, under umbo; cardinal arch in right valve 

 complete, and the hinder part of posterior cardinal rising into a sharp 

 peak ; pallial sinus short and rounded. 



In conclusion, I desire to express my gratitude to Dr. J. C. Melvill 

 and Mr. J. J. MacAndrew for the loan of many specimens from their 

 respective collections, for without this kind assistance I should not 

 have been able to examine so many different species of these genera. 

 I have also to thank Dr. Melvill for reading this paper in MS. and 

 for testing the practical applicability of the descriptions and definition 

 herein set forth. 



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VOL. X. — SEPTEMBER, 1913. 24 



