CALCAREOUS SPONGES, 755 



This genus may be regarded as derived from some more 

 primitive type of Grantessa by the addition of colossal longitudinal 

 oxea to both dermal and gastral cortices. Those in the gastral 

 cortex are probably to be regarded as having been derived from 

 the oxea of the oscular fringe, by downward extension. In the 

 only known species microxea are present, and the articulate tubar 

 skeleton still persists. 



The only known species is : — 



1. A. PAULiNi Hanitsch. 



Amphvute j)aulini Hanitsch [1894]. 



Genus 21. Yosmaeropsis Dendy [1892 B]. 



Diagnosis. Canal system sylleibid (or leuconoid ?). Skeleton of 

 the chamber layer composed of the centrifugally directed 

 rays of subgastral sagittal ti-iradiates and the centripetally 

 directed rays of subdermal pseudosagittal triradiates, which 

 may be supplemented or partially replaced by confused 

 triradiates. No colossal longitudinal oxea. 



For illustrations of this genus see Dendy [1892 B]. 



In all the known species of Vosmaerojjsis we find that the 

 canal system has not developed beyond the sylleibid condition, 

 and there can still be distinguished in the chamber layer very 

 clear indications of an inarticulate tubar skeleton ; in fact, the 

 genus seems to have reached almost exactly the same level of 

 evolution as Megapogon in the Grantiidse, when allowance is 

 made for the different type of skeleton in the two families. 

 This would at any rate seem to suggest that the family Heteropiidse 

 is of comparatively recent origin, and that more complex forms, 

 comparable to the higher types of the Grantiidse, have not yet 

 made their appearance, unless, indeed, they have merely escaped 

 observation. 



We recognise the following species in this genus : — 



Section A. With large oxea and microxea. 



1. Y. DEPRESSA Dendy. 



Yosmaeropsis depressa Dendy [1892 B]. 



2. Y. MACERA Carter. Type species of the genus. 



Heteropia maoera Carter [1885-1886]. 

 Yosmaeropsis m^acera Dendy [1892 B]. 



3. Y. wiLSONi Dendy. 



Yosmaeropsis wilsoni Dendy [1892 B]. 



Proc. Zool. Soc— 1913, No. L. 50 



