GENUS EUGLYPHA— EUGLYPHA ALVEOLATA. 209 



Jus is almost always evenly dome-like, and only in some small forms have 

 I observed it to be sub-acute. In transverse section, the shell is circular, 

 and is rarely somewhat oval, indicating slight compression of the shell. 



The mouth is circular, and is bordered with from four to a dozen angu- 

 lar, minutely serrulated points. The number of these points appears to hold 

 no proportion with the size of the shell, for though usually the smallest 

 kinds have fewest points, they sometimes have as many as the largest kinds. 

 The points or denticles of the mouth are acute, and the minute serrulations 

 on the sides have seemed to me usually three or four ; but in the smaller 

 forms of Euglypha I could not detect them. 



In the larger and the largest forms of Euglypha alveolata, the shell is 

 clearly seen to be composed of regular plates of nearly uniform size. In 

 the smallest forms, the areolate structure of the shell is more or less obvious, 

 but often obscurely defined. Where the definition of the plates and their 

 arrangement is distinct, they have ordinarily appeared to me, as with some 

 previous observers, Wallich, Carter, and Schulze, as of oval form, arranged 

 alternately in longitudinal rows and overlapping at their contiguous bor- 

 ders. This arrangement produces the impression of hexahedral areas 

 defined by zones of smaller elliptical areas. 



In some large individuals of Euglypha alveolata, in which the structure 

 of the shell was unusually well defined, as seen in figs. 2-4, 6, the plates 

 appeared to be ovate, or somewhat cordate, and broader above, where they 

 exhibited a minute median point. In some broken specimens of shells, this 

 description of the plates seemed to be especially obvious. 



From the sides of the fundus of the shell in the largest or best developed 

 forms of Euglypha alveolata, there project from four to six thorn-like spines, 

 as represented in figs. 1-10. The spines are of variable length, usually 

 situated equidistant, and in the same individual about on the same level. 

 In different specimens they may be on different levels, and are more or 

 less divergent, though sometimes convergent, and rarely nearly straight, 

 or in the same line as the long axis of the shell. Sometimes they are in 

 greater number and irregularly placed, as seen in figs. 6-8. They are 

 occasionally obsolete or altogether absent. In the smallest, forms,' and even 

 in the largest, as they occur among alga? and the roots of mosses in damp 

 situations, the shells are almost invariably destitute of spines. Figs. 11-14. 



The conspicuous spines of the fundus of the shell of Euglypha alveolata 



14 RHIZ 



