172 Trans. Acad. Sci. of St. Louis. 



curved subcylindrically from a dorsal to a ventral direction, 

 and the area between the plication and the hinge-line being a 

 triangular, twisted, somewhat concave surf ace, faintly marked 

 by lines diverging from the beak to the posterior boundary. 

 Entire surface covered with fine irregular striae parallel with 

 the basal and anal margins." 



Length of the type specimen 161 mm., height 7 mm., con- 

 vexity of one valve 3 mm. 



Spathella phaselia (Win.). 



PI. XV. f. 10. 



Orthonota phaselia, Bull. U. S. G. S. 153: 399. 



Shell subelliptical in outline, beaks inconspicuous, nearly 

 terminal, but little elevated above the slightly arcuate hinge- 

 line. Ventral and dorsal margins subparallel, the ventral one 

 sometimes with a slight sinuation in the middle. Posterior 

 margin truncately curved below, broadly rounded above, the 

 most posterior extension of the shell above the middle. 

 Anterior margin rather sharply rounded with a deep lunette 

 above. Shell inflated throughout nearly its entire length, 

 greatest convexity a little in front of the middle. Anterior 

 muscular impression shallow, close to the anterior margin of 

 the shell; posterior impression not recognizable. Surface 

 marked by a few more or less inconspicuous concentric lines 

 of growth. 



Length 9 mm., width 5 mm., convexity of a single valve 

 11 mm. 



Remarks. The specimen here illustrated is the type of the 

 species. Its generic position is uncertain, but it certainly is 

 not Orthonota, the genus in which it was originally placed by 

 Winch ell. It is here placed with some hesitation in the genus 

 Spathella. The species has some resemblance to members 

 of the genus Modiomorpha, but is relatively more elongate 

 and narrower posteriorly than the more typical representatives 

 of that genus. 



NUCULA IOWENSIS W. & W. 



PL XV. f. 8-9. 



Nucula houghtoni, Bull U. S. G. S. 153: 378. 



Original description. " Shell small, subovate or subtri- 

 angular in outline, very ventricose. Beaks situated near the 



