188 CrvIBlULINID^E. 



pronounced condition of certain parts (e. c). tlie radiating 

 ribsj the central line, the umbo) , are of slight importance, 

 while the leading features are common to both and con- 

 stant*. 



C radiata, as now defined, exhibits a wide range of 

 variation in what may be called its secondary characters. 

 The cells are sometimes much rounded and widened below, 

 sometimes regularly ovoid ; frequently they are produced 

 below into a point; they also vary much in size. The 

 inclosed triangular space below the mouth is more or less 

 marked; at times it is altogether absent; but there is 

 always a smooth space between the inferior margin and 

 the ribs. The median pore is sometimes wanting ; when 

 absent there are usually two or three large punctures just 

 below the mouth. In certain fossil varieties there is a blunt 

 tubercle on each side of the central pore. 



The zoarium also varies much in its general appearance. 

 In some cases {radiata form) it is of extremely delicate 

 texture, silvery and shining ; in others [innominata form) it 

 is of much coarser make, and of a brownish colour. The 

 area traversed by the radiating furrows is larger or smaller, 

 ovate or subcircular, at times surrounded by a very 

 considerable tract of smooth cell-wall. The umbo, below 

 the orifice, is in some cases largely developed, in others 

 abortive. The same is the case with the central keel. In 

 some forms it all but disappears, and the furrows seem 

 almost to pass continuously from side to side. The ridges 

 or ribs are often very inconspicuous, while in other cases 

 they are strongly defined, radiating from a distinct keel, 

 and standing out prominently round the edge of the area. 



* " I have some doubts wlietlier these two (i. innominata, Johnst., and 

 L. radiata, Moll.) may not, sti-ange as it may seem, pi'ove to be varieties of 

 each othei", in which case Moll's uamc will, of course, have precedence." — 

 Busk, Zoophylology, Quart. Jouru. Micr. Sc. viii. ji. 28o. 



