CRITICAL NOTES ON SOME SPECIES OF 

 DIATOMACE^. 



Amphiprora (?) complexa, Gregory, Clyde Diatoms.— This very 

 singular form was doubtfully placed in the genus Amphiprora, by 

 Dr. Gregory, who remarks that the remarkable structure of this 

 species may render necessary the establishment of a new genus. 



It is somewhat surprising that so acute an observer as the late 

 Dr. Gregory should have placed this form in the genus Amphi- 

 prora, to which it bears no structural affinity. He was also in 

 error in describing it as complex. His specific character is as 

 follows : " frustule, composed of two arcuate and constricted seg- 

 ments, which are broad and thick at the outer margin, thin at the 

 inner margin, and placed opposite each other with a narrow interval 

 between them. Over the middle of these two lateral segments a 

 complex mass, formed of five or six segments, converging inwards 

 and on the ends, like the segments of an orange or melon." 



Fig. 2. 



Fig. 3. 



This description of the frustule is correct to a certain extent ; 

 the valve is not thicker at the convex than at the concave margin'. 

 An ideal transverse section of a single frustule (fig. 1) will explain 

 the apparent thickness of the convex margin, a a valves, the 

 dotted hues b b', the cingulum or connecting zone, as the greatest 

 development of the cingulum takes place at b (fig. 2), the frustule 

 gradually assumes a spherical form ; in the meantime new valves 

 are being formed within the frustule, the margins of which produce 

 the complex appearance previously alluded to. Fig. 3 represents 



