Mr. H. J. Carter on the Polytremata. 187 



" Supplement " (/. c. p. 419), in which the opinion just stated 

 was not retracted, and the following inserted respecting the 

 separation of Garpenteria from Polytrema, viz. : — "Carpenter 

 had no inducement to discuss the question whether Polytrema 

 produces spicules and is thus allied to Carpenteria^ as his spe- 

 cimens contained no sincule$ in their interior. Nevertheless 

 he mentions having seen specimens with the surface entirely 

 covered with a parasitic sponge, the spicules of which, however, 

 penetrated scarcely if at all into the interior of the chambers. 

 By this means Carpenter establishes a sharp distinction between 

 Polytrema and Garpenteria.'''' 



If, then, hereafter it shall appear that the presence of spicules 

 in Polytrema is a common although it may not be a constant 

 occurrence, I might say with Prof. Max Schultze (p. 419), 

 " Perhaps my observations on Polytrema which indicate the 

 remarkable affinity between that genus and Garpenteria may 

 serve to shake Carpenter's faith in his opinion." 



In 1870 Dr. Carpenter, with his wonted generosity, gave 

 me some specimens of Po/y^rema, which, after examination, led 

 me to tlie views expressed in the 'Annals ' of that year (vol. v. 

 p. 391), viz. that under the circumstances it was not strange 

 "that the spicules which to-day are matted among its \Poly- 

 trema^^ pseudopodia, on its surface, should in a few days after 

 be found in the interior of its calcareous structure." 



. These " views " I can now substantiate from the possession 

 of specimens which present the features about to be noticed 

 in the following description of Polytrema miniaceum. 



Polytrema, gen., Bisso, 1826. 



Test fixed, solitary or grouped. Composition calcareous. 

 Structure cancellous, presenting a polygonally divided surface 

 with foraminated interstices, and internal cavities which com- 

 municate with the exterior by one or more apertures. Cavities 

 often containing few or many siliceous spicules entire and 

 fragmentary, derived from different kinds of sponges. 



Polytrema rniniaceumjB])., De Blainville, 1834. 

 PL XIII. figs. 1-6. 



Test fixed, calcareous, solitary. General form massive, 

 rising from an irregularly circular or lobed, root-like, expanded 

 base, passing into a round stem, which soon divides into a 

 head composed of a variable number of expanded short 

 branches, that speedily terminate in more or less compressed 

 divisions, each of which ends in an irregular row of subsquare 



13* 



