INVERTEBRATE PALAEONTOLOGY. 127 



This genus has no near relations either to Mya or Solen, as the name 

 would appear to imply. Indeed, it differs so decidedly from all of the known 

 genera, either among recent or fossil Mollusca, that it cannot be for a moment 

 confounded with any described genus, unless the Permian and Carboniferous 

 forms, for which Professor King proposed the name Janeia, are really distinct 

 generically, which I have suspected may be the case; all hough Professor 

 King has withdrawn the latter name, under the impression that it is really 

 synonymous with Solemya. 



The reason for believing that the name Janeia may possibly yet have to 

 be retained for the Palaeozoic species usually referred to Solemya (or, at any 

 rate, for apart of them), is, that all of the American Carboniferous species of 

 this type that I have seen, differ from the recent species of Solemya in not 

 being exactly equ'walve; that is, although apparently exactly like that genus 

 in all other respects, they seem to have the beak of the left valve always 

 lapping upon that of the right. For a long time I thought this merely due 

 to accidental distortion ; but after seeing numerous specimens, some of which, 

 from the even adjustment of the ventral margins of the valves, as well as from 

 their general appearance, seemed not to have suffered any distortion, and yet 

 showing this character, I have been led to believe it natural; and as the 

 living typical species of Solemya have the beaks equal, it is not altogether 

 improbable that there may be a generic difference between them and the 

 Palaeozoic species. It is true, however, that Professor King did not mention 

 any such inecjuality of the beaks as one of the characters on which he pro- 

 posed to separate Jan cia ; but it is a character that might readily be over- 

 looked, from the supposition that it was due to accidental distortion. If 

 the name Janeia should have to be retained for the whole or a part of the 

 Palaeozoic species usually referred to Solemya, the latter would most readily 

 be distinguished by this difference in the character of the beaks. 



The Carboniferous genus Clinopistha, Meek and Wothen, is also related to 

 Solemya, with which it agrees in the thinness of the shell, the character of 

 the muscular impression, and in having its beaks nearer the shorter side of 

 the valves, as well as in the nature and position of its ligament. It differs, 

 however, remarkably in form, being a short gibbous shell, truncated behind, 

 with both ends closed. If also differs in showing the same inequality of the 

 beaks seen in the Palaeozoic forms usually referred to Solemya ; from which 



