212 Mr. H. J. Carter 07i the Polytremata. 



or less continuous internal cavity, although very thin, with 

 superior aperture, allies this Foraminiferous test much more 

 to Polytrema than to Planorhulina, although its marginal cells 

 very much resemble those of the latter. Having only one 

 specimen, and not liking to destroy any part of it, what I have 

 stated concerning the " single " aperture (fig. 18, c) and 

 " continuous " internal cavity must be considered provisional. 

 The latter may be in chambers corresponding with the reticu- 

 lation on the surface, and therefore divided ; or it may be sup- 

 ported by pillars, as in Polytrema miniaceum^ and thus more or 

 less continuous. 



On the surface of the specimen is a small group of pink 

 PlanorhuUna-uixvAQS. (fig. 18, (^, which in their form and much 

 larger size, together with their foramina, contrast strongly with 

 that of Polytrema planum. I have also specimens of Poly- 

 trema miniaceum respectively growing upon colourless patches 

 of Planorhulina^ but never saw Planorbuliua either colourless 

 or pink growing by the combination of its utricular cells, or in 

 any other way, into the form oi Polytrema miniaceum ; hence 

 I agree with Dr. Carpenter {op. cit. p. 209) that Max Schultze's 

 Acervulinida are nothing else but pink varieties oiPlanorhu- 

 lina (Max Schultze, ' Polythalamien,' 1854, p. 67, pi. xvii. 

 figs. 12-15). 



EXPLANATION OF PLATE XIII. 



Fig. 1. Polytrema miniaceum, De Blainville, uat. size. 



Fig. 2. The same. Central portion of basal layer, about 2-48tlis incli in 

 diameter, viewed from the outside, showing : — a, confused ar- 

 rangement of primary chambers ; ft, three circular rows of ra- 

 diating lines with oblong quadrangular interspaces ; c, portion 

 of basal layer i*eflected, to show foraminated roof of circular 

 cavity. Scale l-96th to l-8.30th of an inch. 



Fig. 3. The same. Diagram of horizontal section of fragment, to show 

 relative position of foraminated (^"spiral") layers, a a a, and 

 hollow pillars of support, b b b. 



Fig. 4. The same. Embryonic form, nearly l-80th inch in diameter at the 

 base and l-83rd inch high, broken out at the side, showing: — 

 a, base expanded and foraminated ; b, cylindrical stem or process, 

 also foraminated ; c c, broken edges of foraminated layer ; d, thin 

 superior or growing portion of the same ; e, cancellated structure 

 of interior; /, siliceous spicules of sponges projecting from the 

 interior. Scale l-12th to l-830th of an inch. 



Fig. 5. The same. Truncated end of embrj^onic form, on the same scale, 

 just where the cancellated structure commences, showing the 

 relative position, number, and size of the cavities at this point. 



Fig. 6. The same. Diagram of head, to illustrate description : a a a a, 

 branches entire ; b b, ends of branches broken off; c c c, apertures 

 of entire branches ; d d, external or foraminated surface ; e, in- 

 ternal structure ; ///, young foraminated layer; gg g, dimples 



