of Microscopical Org-anisms. 339 



dulate ; in side view broadly elliptic ; costa? conspicuous, 

 short, and radiant. 



Hab. Para River, at Una. 



This singular form was assigned by its discoverer to the 

 genus Surirella, but I have now no hesitation in transfer- 

 ring it to the allied genus Campi/hdiscus. One of the 

 chief points of interest in this species is the great width 

 attained by the central or interstitial portion, which, in this 

 genus, as in the Coscinodiscece, is usually reduced to a 

 narrow ring. It resembles Surirella Campylodiscus in some 

 respects, and a comparison was suggested by its discoverer 

 to S. striatida, Turp., but I think it is certainly entirely 

 distinct from either. 



Figs. 41-45. DicLADiA ? mamillana. Bail., nov. sp. 

 Smooth ? valves sometimes equal, sometimes unequal ; 

 mammillated, turgid ; one or both valves with conical 

 mamillae connecting at the base ; valves separated by a 

 median band not striated (?) ; styles and spines wanting. 



Var. a. Valves with two cones on one side, and none 

 on the other. 



p. Valves with only one cone on each side. The lat- 

 eral view resembles a Hyalodiscus. 



y. Valves with one cone on one side, two on the other. 



h. Valves with two cones on each side. 



This species, which is doubtfully referred to the genus 

 Dic/adia, con'esponds very closely to some stages of growth 

 in Dicladia capreoliis, as figured by Brightwell, Mic. Jour- 

 nal, Vol. IV. page 105. Moreover, Fig. 74 of the 2d 

 Plate seems also to be but a stage of growth of Dicladia 

 capreolus, from which the lower valve has been broken 

 off. The latter are quite common in these soundings, and 

 were figured by my father as species of Chcetoceros. I 

 am, however, disposed to regard them all as stages of 

 growth of Dicladia capreolus. The number of mamillaB 

 varies from one on each side to two on each side. The 



