332 Mr. H. J. Carter on the Structure of the Foraminifera. 



it becomes questionable, after all, whether the cyclical and helical 

 characters are of much use in classification ; but to this point 

 we will return again after having alluded to the other genera of 

 Foraminifera in which I shall have to describe species. 



Orbitolina, D'Orb. 



Of this genus I have nothing to add more than is stated under 

 the species which I have described. 



Cyclolina, D'Orb. 



This now appears to me to be a species of Orbitolina, which, 

 had it been better defined by D'Orbigny, would have saved me 

 from much error, as will be observed by my " Observations " 

 under the head of " Orbitolites pcdunculata " at the end. 



Heterostegina, D'Orb., and Cycloclypeus, Carp. 



Under these names respectively will be found a description of 

 the specimens of Heterostegina and Cycloclypeus which, with 

 Orbitolites Mantelli, I found together on the south-east coast of 

 Arabia. 



Of the former I have nothing to add here; but as regards 

 Cycloclypeus, from existing specimens of which Dr. Carpenter 

 has given his excellent description and illustration of the genus 

 (Phil. Trans. 1856, p. 555, &c.), one cannot help seeing, in the 

 oblong form of the chambers, the irregularity of the rows, their 

 cyclical arrangement, their vertical thickness diminishing towards 

 the circumference, each chamber being connected with two be- 

 hind and two before it, the canal-system, and, lastly, the conical 

 non-tubular parts of the test, which resemble the columns, that 

 Cycloclypeus approaches Orbit aides dispansa as nearly as Oper- 

 culina approaches Nummulites. 



In my description of the minute structure of Orbit oides dis- 

 pansa, I have stated that I was not able to see such an elaborate 

 disposition of the canal-system ; but then the size of the recent 

 specimens of Cycloclypeus examined by Dr. Carpenter, and their 

 structure generally, far exceeding, in both, the infiltrated speci- 

 mens of Orbitoides in my possession, may partly, if not wholly, 

 account for this. 



For further observations on the specimens of Heterostegina 

 and Cycloclypeus which have come under my notice, see their 

 descriptions respectively. 



Orbiculina and Orbitolites. 



The exhaustive and valuable researches of Dr. Carpenter on 

 these two genera, given in the 'Philosophical Transactions' for 



