42 One Tlwusand Objects 



This genus differs from the last in the central nodule 

 being widened into a clear central band. The present is 

 a small species, with somewhat spear-shaped valves and 

 obtuse extremities. It occurs in salt-water marshes. (PI. 

 IV, fig. 20.) 



300. BEAUTIFUL STAURONEIS (Stauroneis pulchelhi) has 

 also spear-shaped valves; but the central band is dilated 

 outwards, and the stria; are much more distinct than in 

 the last. It is common in sand ripples, as well as in 

 dredgings. 



301. LOZENGE-SHAPED PLEUROSIGMA (Pleurosigma 

 quadratuni). In this genus the valves are more or less 

 spear-shaped (lanceolate), with a sigmoid line (shaped 

 like a long s down the middle. The form of the pre- 

 sent species is rhomboid, and easily distinguished by its 

 angular shape. The striae are oblique and delicate. It 

 is common in salt-water ditches and small creeks. 



302. ANGULAR PLEUROSIGMA (Pleurosigma angulatutri) 

 is not of so angular a form as the last; but the stria? are 

 similar, and it is found in kindred localities. 



303. LONG PLEUROSIGMA (Pleurosigma elongatuni) is 

 long and narrowly spear-shaped, with the median line 

 almost straight. The stria? are oblique. The long narrow- 

 form of this species is sufficient to distinguish it from its 

 allies. 



304. BALTIC PLEUROSIGMA (Pleurosigma Balticuni). 

 The valves are long and straight, except near the extremi- 

 ties, which are curved in opposite directions. The striae 

 are both longitudinal and transverse. Occurs in salt 

 marshes. 



305. CROSS-LINED PLEURISIGMA (Pleurosigma strigilis). 

 ' This form is spear-shaped (lanceolate), with transverse 

 and longitudinal striae, which are very distinct. The 

 difference in the shape of the valves must be observed in 

 distinguishing this from the last. It is also found in salt 

 marshes. 



306. ACUMINATE PLEUROSIGMA (Pleurosigma acumi- 

 natuni) is spear-shaped or lanceolate, but with more 

 obtuse extremities than the last. The striae are both 



