THE NAIADES OF MISSOURI 



155 



St. Lawrence system; Red River of the North; Eastern Texas 

 and Cumberland River. 



Lasmonos simpsoni (Ferriss). 



(Simpson's vShell.) 

 PL XXVI, Figs. 91 A and B. 

 1900 — Lampsilis simpsoni Ferriss, Nautilus, xiv, p. 38. 



Animal Characters unknown to writer. 



SHELL CHARACTERS. 



External Structures: — Shell subovate, elongated, sub- 

 solid, narrowly rounded in front, broadly rounded behind, some- 

 what alated; disk smooth; beaks low, sculptured b}^ ridges some- 

 what corrugated and nodulous; epidermis tawny with green rays 

 with rather roughened growth lines; hinge line evenly curved. 



Internal Structures: — Cardinals reduced to mere stumpy 

 rudiments; laterals single in right, very faintly double in left 

 valve; anterior scars rather deep, posterior shallow; nacre bluish 

 shaded with violet, copper or pink. 



Sex Length Height Diameter Locality 



cf 78 X 46 X 28mm. (White R., Hollister) 

 9 95 X 50 X 22 " ( " " " ) 



Miscellaneous Remarks: — No juveniles, nor young shells, 

 have been obtained by the writer in this State. However, Mr. 

 Ferriss, the author, has obtained a good suite from Spring River, 

 Hardy, Arkansas, and has described the young shells as possessing 

 an epidermis with green rays and "coppery beaks," a well marked 

 post-umbonal ridge and low but distinct beaks with coarse corru- 

 gations. The author of this species, groups it between Lasmonos 

 fragilis and leptodon. From the former it may be distinguished 

 by a thicker more elongated shell, by more reduced hinge teeth 

 and less varigated nacre and from the latter by being more inflated, 

 wider, thicker, not so pointed posteriorly and with fewer rays. 

 Hence its place can be fairly weU determined conchcologically. 

 Future studies of its marsupial and glochidial characters of this 

 species, as well as that of leptodon (=5. ieniussimus Lea), may 

 classify it far differently, since shell characters are too liable for- 

 parallelism and convergence as true bases of classification. 



