GENUS ORBirOlDES. 303 



the same distinctness. It seems to form a reticulation which includes each chamberlet in 

 one of its meshes, as shown in fig. 5 and in the lower part of fig. 9 ; but I have not been able 

 to satisfy myself of the existence of distinct annular canals.* 



508. Affinities. — In the general plan of structure of Orbifoidefi we are reminded on the one 

 hand of Ci/cloclj/pci/s (Plate XIX, fig. 2), and on the other oi Nnmmiilina (Plate XVIII, fig. 9) ; 

 for (as will be apparent on a comparison of the figures just referred to) if the superficial 

 chambers of an Orbitoides were obliterated by the approximation of their laminse, it would be 

 converted into a Ci/cJocIypeus ; whilst, on the other hand, if its growth were spiral instead of 

 cyclical, it would come to resemble one of those Kiunmidinm in which the alar prolongations 

 of the chambers have been broken-up into insulated chamberlets by the inosculation of their 

 septa. This is much more than a mere superficial resemblance, such as exists between the 

 arrangement of the chamberlets of the median plane in Cyclodypcus or Orbitoides, and that of 

 the chamberlets of the disk of the simple type of Orbitolites ; the affinity of Orbitoides to 

 Ci/clocli/peus and to Niciiimidina being marked by its approximation to those types in all the 

 characters which have been heretofore specified as of the most fundamental importance, such 

 as the minutely tubular structure of the shell, the doubleness of the septa (each chamber 

 possessing its own proper wall), and the interposition of a canal-system between their two 

 lamellpe. In all these particulars it is equally removed from Orbitolites, with which it has 

 nothing whatever in common save its cyclical plan of growth, and the mode of communication 

 between the chambers of its median disk which appears to exist in 0. Mantelli.-\ In the 

 arrangement of the chamberlets of its superficial laminae, Orbitoides is so closely related to 

 certain forms of Tinoporus (Plate XV, figs. 3, 4), that if the chambers of the latter were 

 more compressed vertically, and were more completely differentiated from those of the median 

 plane, they would resemble those of Orbitoides in every essential particular save the want of a 



* In the description of the canal system of 0. Mantelli given by Mr. Carter (xxiii a, p. 330) 

 there seems to me a confasion which I am unable to unravel, between the apertures which connect 

 the cavities of the chambers and gave passage during life to stolons of sarcode that united the segments 

 of the body, and the system of interseptal canals which has little connection with the cavities of the 

 chambers, being confined to the spaces between the two lamellae of their partitions. 



t I must confess myself at a loss to understand the grounds on which Mr. Carter considers that 

 0. Mantelli should be removed from this genus and placed in near proximity to Orbitolites, though he 

 would no longer (as formerly) rank it with that type. There is absolutely no difference that I can 

 discover between the superficial layers of the 0. Fortisii and the O. Mantelli ; the diflerence between 

 the forms and proportions of the chamberlets of the median plane iu these two types are clearly of 

 not more than specific value, even if they amount to that ; and if there should prove to be a lateral 

 communication between the chamberlets of O. Mantelli which does not exist between those of 

 O. Fortisii, and the canal-systems in the two types should prove to be distributed on distinct plans 

 such differences would assuredly not render necessary the generic separation of organisms which 

 resemble each other so closely in all other respects. In approximating 0. Mantelli to Orbitolites, it is 

 clear that ]\Ir. Carter has not appreciated the grounds on which Orbitoides and Orbitolites are placed, 

 according to the plan of classification jointly adopted by ^Messrs. Parker, Rupert Jones, and myself, in 

 two different primary divisions of Forarainifera. 



