542 PLANKTON OF THE SVDNEY WATER SUPPLY, 



P. Orr-ei Huitfeldt-Kaas, or P. iiiconspicuum Leinm. If these 

 intermediate forms are not noted, it is only because a sufficient 

 quantity of material has not been obtainable. 



Perid. TABULATUM(Ehr.). (PI. Ivii., figs.1-3). 



Long. 42-44; lat. 42 /x. No. 115. 



Two specimens were noted, globose, with typical areolate mem- 

 brane. The disposition of the plates in the hypovalve was almost 

 exactly the same as in our var. yramilosum; while their arrange- 

 ment in the epivalve was strikingly like that in var. Westii. 

 Compare PI. Ivii., f.2, with Pl.lv., f.2a and ic; and PI. Ivii., f.3, 

 with PI, Iv., f 6. The disposition of the vertical and transverse 

 furrows, on the reverse, answered perfectly to that in PI. Iv., i.bb. 



Var. GRANULosuM, n.var. (PI. Iv., figs. 1-4). 



P. globosum vel ovatum, ut in forma typica, tam longum quam 

 latum vel paullo longius, 60-76 /x longum, 5.3-76 fi latum; mem- 

 brana minute delicatissime granulosa; granulis irregulariter vel 

 in striis longitudinalibus dispositis(Pl. Iv., f.2). Epivalva conica 

 vel rotunda; apice interdum crena, vulgo praeterea dentibus binis 

 instructa; tabulis sequatoriis 7, tabulis apicalibus semper plus 

 minus irregulariter dispositis. Hypovalva rotunda; intei'dum 

 margine posteriore concavo, ssepe dentibus vel spinis minutis 

 binis utrinque ornato; tabulis a^quatoriis 5, antapicalibus 2; fossa 

 longitudinal i valde dilatata. 



The granulation is very often in indistinct longitudinal lines — 

 a hint that it is the origin of the following form. The intercalary 

 zones are, in this variation, generally reduced to a mere ridge, 

 even in specimens of the largest size, showing that growth has 

 been taking place in all parts of the membrane, and not at the 

 intercalated strips only, as has been supposed. It is probably 

 this general growth of the cell, as a whole, that has prevented 

 the formation of the incrassate, areolate membrane of the type, 

 which is very much smaller. 



Var. WKSTn(Lemm.) mihi, forma australis, n.f. 



(Pl.lv., figs.o-9). 

 Long. 44-54; lat. 42-59 /i. 



