328 



Microporella Hincks, char, emend. 

 Diporula Hiiicks, Fcnestriilina JuUien. 



The zou'cia, which may have up to 7 spines, possess a vestibular arch, devel- 

 oped to a varying extent, and a semicircular aperture provided with a straight or 

 very slightly concave proximal rim. In most species there is within this and in 

 the whole of its breadth a higher or lower supporting beam as support and 

 attachment for the operculum. The latter is simple, more or less chitinized 

 and provided with a muscular process within each lateral margin. A peristome 

 is wanting or only weakly developed. One or two lateral heterozooecia are present 

 and a median ascopore, proximally to which there may often appear a tubercular 

 projection. Multiporous pore-chambers occur as a rule and the ocecia consist of a 

 calcified endoorecium, which as a rule has no pores, and a membranous or 

 partially calcified ectoooecium. 



The two genera Escharina and Microporella show such great agreement in 

 their structure, that there can scarcely be any doubt that the former must be 

 regarded as the mother-genus to the latter, and the greater or smaller resemblance 

 which various Escharina species show to corresponding Microporella species, would 

 seem to indicate that the transformation of an Escharina species to a Microporella 

 species has occurred several times. Apart from the variation occurring in both 

 species, the resemblance between Escharina spinifera and Microporella ciliata is so 

 great, that we might well consider that the latter has descended directly from the 

 former. The two species thus agree in the number of oral spines, in the i)osses- 

 sion of scattered pores, an avicularium and of three elongated pore-chambers. In 

 both species there may be a tubercle-like projection proximally respectively to 

 the ascopore and the sinus, and the former quite agrees in form with the prox- 

 imal part of the sinus. Further, the ocEcia agree, and the supporting beam in 

 Mic. ciliata might be considered as having arisen by a fusion of the two long 

 hinge-teeth in E. spinifera. The supporting beam mentioned is for the rest weakly 

 developed in Mic. ciliata (PI. XV, fig. 5 b), whilst it reaches its greatest develop- 

 ment in Mic. marfjinata (PI. XV, fig. 3 b). It seems to be quite wanting in Mic. 

 Malusi (Pi. XV, fig. 7 a). Two other species which also show essential agreement 

 are Escharina pes anseris and Microporella /lahellidera n. sp., but the difierences 

 between them are too great to permit us to conclude that the latter has come 

 directly from the former. They agree amongst other characters in possessing vibra- 

 cula and endozooccial ocecia, and in both there may be a tubercle-like project- 

 ion, which has its flat surface directed towards the aperture. Whilst in this genus 

 there is as a rule a membranous ectoooecium, the arched calcified ridge which 



