NEBBLA CAEINATA. 107 



from the margin as a flattened wing, and is of uniform 

 thickness throughout. Usually the polygonal surface- 

 markings are also faintly carried OYer the surface of 

 the carina. 



In most examples the plasma is more or less crowded 

 with minute colourless globules and chlorophyllous 

 food-particles. From the density of the granular proto- 

 plasm the pale nucleus is often hardly discernible. 

 The body occupies usually the entire cavity of the test 

 or nearly so. 



A glance at the figures on Plate XXVI will show the 

 great variability of the test of N. carinata, particu- 

 larly in the degree of development of the carina and 

 in its outline when the test is viewed on its broader 

 surface. Not infrequently- it has an outline, as figured 

 by Penard (' Faune Rhiz. Leman,' p. 357), not unlike 

 that of JSf. collavis, and similarly proportioned. Leidy 

 ('Freshw. Rhiz. N. Amer.') represents it as being some- 

 what broader in proportion to the length, the wing 

 more expanded and the mouth terminating a short 

 neck. Cheshire examples for the most part exhibit 

 the wing still more expanded laterally, making the 

 breadth of the test, over all, nearly equal to the 

 length, the lateral edges, from a broadly-arched 

 crown, descending in straight lines down to the con- 

 tracted mouth, which usually terminates a short neck 

 (PL XXVI, fig. 5) ; whilst in other and more rare 

 examples the general contour of the test is rotund, 

 like that of N. tin eta, also with a short neck 

 (PL XXVI, fig. 9). The latter might almost be 

 regarded as a distinct variety-, but we are not satisfied, 

 from the few examples as yet examined, of its perma- 

 nence. Examples gathered in Merionethshire corre- 

 spond closely to the Dunham ones (PL XXVI, fig. 8). 



These different forms indicate a wide range of 

 variability. Probably they are determined by the 

 degree of development of the carina and have no 

 specific or varietal significance. 



