Mr. H. J. Carter on the Structure of the Foraminifera. 31 L 



Natural History ;' and hence the reasons for Prof. Williamson's 

 discovery having been omitted. 



Further Observations on the Structure of Foraminifera. 

 Operculina, D'Orbigny. 



In Dr. Carpentei''s elaborate and valuable paper on the struc- 

 ture of this genus, taken from specimens of Operculina arabica 

 originally obtained from the Philippine Islands, he has made an 

 important addition to what I have stated on the subject in one 

 respect, and anything but one in another, inasmuch as he has 

 denied the spicidar structure of the marginal cord, which is one 

 of the most palpable objects in the test. 



The important fact that he has added is the discovery, in the 

 canal-system, of a main spiral trunk, which commences with the 

 spire, in duplicate (that is, one in each horizontal half of the 

 test), and follows it to its termination. These two large trunks, 

 to which Dr. Carpenter has applied the name of " spiral canals," 

 he states, " though only running along the angles of the mar- 

 ginal cord, pretty obviously communicate with the plexus of 

 passages which it contains ; and thus the interseptal system of 

 one whorl is brought into direct connexion with that of the pre- 

 cedmg*." To complete this description, I would add that, in 

 the first two or three turns, the interseptal canals form a direct 

 bond of union between the spiral canals, but afterwards only by 

 some of their branches, as the interseptal canals then go to the 

 inner side of the marginal cord, where they di\-ide into branches, 

 and the great spiral canals remain continuous outside, at the 

 point of junction of the spiral lamina and the cord. 



I had observed these canals, as may be seen by my illustration 

 (fig. 5, loc. cit.), where the interseptal canals of the outer whorl 

 are represented as springing from one of them, but had not 

 specially recognized them as they deserved, and as has now been 

 very fortunately done by Dr. Carpenter. But MM. D'Archiae 

 and Haime had recognized and figured them, without knowing 

 what they were, even before this, in Nummulites planulata (pi. 9. 

 fig. 7, p. 63), where they state, with reference to "the grooves" 

 in the marginal cord, " Une seule espece {N. planulata) offi-e de 

 chaque cote du bourrelet un sillon environ cinq fois plus large 

 que tons les autres. Les canaux moyens s'ouvrent presque tou- 

 jours dans ces sillons." No doubt, therefore, exists in my own 

 mind, from having also seen them in a closely allied Nummulite, 

 viz. N. Ramondi (PI. XVII. fig. 15//), that the " sillons " repre- 

 sented in the figure mentioned are the " spiral canals " described 

 by Dr. Carpenter in Operculina. 



* PhU. Trans. 1869, p. 28. 



