Characters o/"Lingula anatina. 15 



ment of the sctal band ; as may be seen by effecting the outer 

 margin (here not attached) of the latter organ, and cutting 

 the pedicle across at the root (fig. 5, h). 



It is scarcely to be expected that any well-defined scar could 

 result from the attachment of the muscular layer, considering 

 the immediate proximity of such scar to those produced by 

 other organs (setal band and corneous layer, see fig. 3), and 

 the liability of all the scars to become confluent through the 

 incremental creeping backward or forward, as the case may be, 

 of the organs respectively producing them. Were it otherwise, 

 the attachment of the setal band and the corneous layer ought 

 to give rise to two subparallel lineated scars, more apart in 

 the middle than at the ends ; while between them there ought 

 to be an ellipsoid, produced by the muscular portion of the 

 pedicle (see fig. 5, h, i). For the reasons stated, the last kind 

 of scar cannot be expected to occur : traces may ; which leads 

 me to imagine that certain lines occasionally to be seen running 

 along the hinge-slope may represent it. An elliptical scar, 

 similarly situated, has been detected by Mr. Davidson and my- 

 self in testiferous specimens of certain Trimerellids : it is clue, 

 we suspect, to the inner muscular layer of the pedicle. 



Conclusion. — My researches connected withLingula strongly 

 enforce on me the belief that it represents a group of Pallio- 

 branchs differing in several very important points from most 

 others of its class. From being furnished with spiral arms, it has 

 been placed by Dr. Gray in his " subclass Helictopoda," along 

 with Rhynclwnella, Spirifer, Productus, and some other related 

 genera ; but as all these belong, from certain evidences which 

 I could adduce, to the great non-aniferous section, whereas 

 Lingula possesses an anal vent, it is clear that Gray's " sub- 

 class " would be made a more natural one by removing this 

 genus from it. 



As regards the great sections to which allusion has been 

 made, they appear to me to constitute the two primary and 

 most comprehensive ones into which the Palliobranchs may be 

 divided. I would therefore propose that one section should 

 comprise all the non-aniferous families belonging to Gray's 

 subclasses Ancylopoda and Helictopoda, with the name Clist- 

 enterata*', and that the other should include the aniferous 

 families Lingzdidce and Discinidw, and be designated Treten- 

 terata\. 



Confining myself to the last section, I shall briefly notice 

 the features which distino-nish it from the first one : — 



*&■ 



* From cleistos, shut, and entera, intestine. 

 t From tretos, perforated. 



