GENUS TINOPOKUS: AFFINITIES. 561 



numerous large pseudopodian foramina*. This relationship is admitted by Messrs. 

 PARKER and RUPERT JONES; who state, however, that Planorbulince are differentiated 

 by having " two or three tubular and margined apertures to each chamber, coarser 

 pseudopodial pores, and no umbilical cells." Now I have shown that every chamber in 

 the adult is connected with its adjacent chambers of the same or of alternate planes by 

 two apertures ; so that at the free growing margin of the young disk there would pro- 

 bably be at least two such pairs of apertures in the wall of every chamber. The 

 difference in the size and number of pseudopodian pores is a very trivial character. 

 And the superposed umbilical cells will probably be absent in the young Tinoporus, 

 when as yet only a small number of rows of chambers have been formed around the 

 central cell. I have, in fact, specimens in my possession which would be unhesitatingly 

 characterized as Planorbulince by such as are unacquainted with the structure of the 

 type we are considering ; yet which I cannot help regarding as in all probability young 

 forms of Tinoporus, having been found in the same dredging, and presenting just the 

 characters which I should expect from analysis of the structure of the adult to find in 

 them. Moreover, I have Planorbulince whose early growth is so distinctly spiral as to 

 correspond in every essential particular with the young of Rotalia. 



218. It is not a little remarkable, however, that this organism should also be very 

 closely related to a body of which the true nature has hitherto been doubtful, viz. the 

 Millepora rubra of LAMARCK-^, the Polytrema miniacea of BLAINVILLE^. This grows 

 parasitically upon shells, sometimes spreading over their surface in a laminated form, 

 sometimes rising into a sort of stem and sending off branches. I have ascertained by 

 examination of thin sections, that it is composed of minute chambers piled together very 

 much in the manner of those of Tinoporus, and having the same kind of communica- 

 tions ; and as Mr. PARKER has in his possession a specimen of a nearly globular form, 

 attached to a projection of a bivalve shell, it may be questioned whether the difference 

 between the two organisms is even of specific value. For the mode of growth which 

 ordinarily characterizes each, shows a tendency to pass into that of the other ; Tinoporus 

 Icecis occasionally flattening itself out and extending marginally, whilst Polytrema 

 miniacea occasionally restricts itself within a compact spheroidal form. The probable 

 relationship of Polytrema miniacea to the Foraminiferous type has been already 

 suggested by the sagacity of Dr. J. E. GRAY ; but as he was not acquainted with the 

 internal structure either of Tinoporus or of Polytrema, he could not make a more 

 particular approximation. I should add that the bodies described and figured by 

 Professor MAX. SCHULTZE|| under the generic name ofAcervulina appear to me to belong 

 to the same type. I have in my possession a specimen growing round the stem of a 



* See Professor WILLIAMSON'S Monograph of the Eecent Foraminifera of Great "Britain, p. 57. 

 t Hist. Nat. des Animaux sans Vertebras, troisieme edit., torn. ii. p. 309. 

 J Manuel d'Actinologie, p. 410, pi. 69. fig. 16. 

 Proceedings of the Zoological Society, April 27, 1858. 

 || fiber den Organismus der Polythalamien, p. 67, plate 6. figs. 12-15. 

 MDCCCLX. 4 E 



