92 



THE NAUTILUS. 



moreover, was found in company with C. transcersa, which it resem- 

 bles in being so elongated. But its beaks are not anterior, narrowt r 

 and less full, the hinge margin is not so straight, and the anterior 

 and posterior ends are rounded, not truncate. 



6. (7. partumeia Say. Widely distributed and decidedly variable, 

 some forms being hardly recognizable. At Garrettsville, Ohio, Mr. 

 Streator has found a form with exceptionally broad, full, rounded 

 beaks, quite unlike those of a Calyculina. 



7. C.jnyeiisis Pr. (Sphaerium jayanum, in Mon. Corb.). One of 

 the rarer species, and known from Indiana and Michigan to Wiscon- 

 sin and Iowa. Seems to be valid. 



8. C. truiicata Linsley. Rather common, and somewhat variable. 

 ]n regard to shape and surface appearance, it usually resembles 

 more C. partumeia than securis. Yet in some forms the posterior 

 end is rather obliquely truncated, and the beaks are rather strongly 

 inclined towards the anterior. The mussel is more inflated, as a 

 rule, than the dimensions given in Prime's description. 



Clessin (Cycladeen, p. 246) says: " It appears to me somewhat 

 doubtful whether C. truncata can be regarded as a good species. 

 Around the type of Cal. securis are grouped several species (Sph, 

 contractum, rosaceum, sp/taericuin, truncation, lenticiilu}, which, ac- 

 cording to European principles, would unhesitatingly be regarded as 

 varieties." In all probability, Clessin had insufficient materials on 

 hand. 1 C. truncata has been collected in many places over a wide 

 territory, and has been found distinct. Quite commonly, I have 

 found C. securis and truncata associated, and the two often also with 

 C. partumeia, C. contracta is evidently of another type. As to 

 rosacea and sphcerica we refer to the following. 



9. C. rosacea Pr. There is a small Calyculina with a thin, trans- 

 parent, horn-colored, or almost colorless shell, narrow, moderately 

 high beaks, which is evidently distinct from the other species. It 

 is known from different places in Michigan, Illinois, New York and 

 Virginia. For years it has been a stumbling block, since most forms 

 did not agree exactly with Prime's description of rosacea, and yet 

 they could not well be ranged under any other species. After all, it 

 seems that they are rosacea. 



1 As directly evident from some of his descriptions and notes. E. g., he say3 

 in the description of C. securis : " shell shining," which is rather an exception 

 than the rule. Some of his descriptions were made from single specimens, &s 

 he states. 



