COEBITELLA AND ITETEROTELLA. 23 



The sponge differs from Specimen A in its much thicker 

 wall and in the more irregular disposition of its skeletal bundles. 

 Striking as is the difference at first sight, I consider it as due 

 to individual circumstances. Not improbably we have here to do 

 with a specimen fully developed in all parts but stunted in general 

 growth. I am inclined to think that the checker-like arrange- 

 ment of the main parenchymal bundles in Specimen A, as also 

 in the corresponding portion of Corbitella pulchra, is related to 

 the relatively young state of the part concerned. After that part 

 has reached a certain stage of development, an irregularity in the 

 arrangement of the bundles may set in, as is factually seen in 

 the lower and therefore the older portion of Corbitella pulchra. 

 This is all the more conceivable in Heterolella corbicula, since 

 here the parenchymalia are totally wanting in large stauractins, 

 whose paratangentially disposed rays might permanently determine 

 the vertical intersection of the bundles. Moreover, if in Specimen 

 A the external oblique bundles should undergo a further quantita- 

 tive development, a great approach in its appearance towards that 

 of Specimen B would be the result. 



As regards spiculation the two specimens are practically 

 identical even to details, so far as my observations go. For this 

 reason I consider it superfluous to enter specially into its de- 

 scription. 



Specimen C. The labelling of this runs : " Alcyoncellam 

 corbicula Val. de Bourbon. Donné par M. Sachet 1857." It 

 is the torn upper end of the body, much mutilated and preserved 

 pressed between two plates of glass. In the middle is the irre- 

 gularly oval sieve-plate, 54 mm. and 68 mm. in diameters. Around 

 this is attached a small adjoining portion of the lateral wall, 



