176 FAMILY GLOBIGERINIDA. 



Genus I.— Orbulina (Plate XII, fig. 8). 



278. History. — The little spherical bodies to which the appropriate name Orhulina was 

 first given by D'Orbigny in 1839 (xcii), had been described and figured by Soldani (ci) 

 under the names Sphcenda pdma and S. Mspida ; but they do not seem to have received any 

 attention from intervening authors. Subsequently to its recognition by D'Orbigny, this type 

 has been generally adopted by systematists as a distinct genus until a recent date, when its 

 claim to that rank has been called in question, on grounds which will be presently explained. 

 Not being as yet satisfied of the invalidity of that claim, but not, on the other hand, feeling 

 able to affirm that the objections to it are altogether groundless, I have thought it best 

 to retain the genus provisionally ; especially since I find that my friends Messrs. Parker and 

 Rupert Jones are in accordance with me as to the propriety of this course. 



279. Externcd Characters and Internal Hlmcliire. — The shell of Orhdina is usually an 

 almost perfect sphere, varying in diameter from l-35th to l-200th of an inch. Its surface 

 is usually roughened by minute tubercles, presenting an appearance which is described by 

 Professor Williamson (ex, p. 2) as " arenaceous ;" but I am satisfied that its substance is not 

 made up of any such aggregation of foreign particles as constitutes the material of the truly 

 " arenaceous'' shells ; whilst, on the other hand, it is only in the earlier stage of its formation 

 that it has the hyaline transparency characteristic of the truly •' vitrer us" shells. The shell 

 is pierced (Plate XII, fig. 8) with a number of large pores, the average diameter of which is 

 about l-1500th of an inch ; their distance from each other varies considerably, but is seldom less 

 than about l-7oOth of an inch. Between these there are very numerous minute pores, not above 

 l-10,000th of a inch in diameter, and closely set together, so as to be pretty uniformly distri- 

 buted. In the large majority of specimens these constitute the only apertures in the globular 

 shell; but we frequently meet with one of larger size, normally round, but sometimes 

 irreo-ular, its diameter averaging l-500th of an inch. I am much disposed, however, to 

 question how far this can rightly be regarded as comparable to the aperture of ordinary 

 Foraminifera ; since, on the one hand, it is often absent ;'•' whilst, on the other, when it exists^ 

 it is only one among the very numerous large pores by which the shell is fenestrated, distin- 

 o-uished from the rest only by its pre-eminent size. I believe the truth to be that the sarcode- 

 body puts forth its prolongations indifferently from any or all the pores ; and that, when this 

 organism multiplies itself by the formation of detached gemmae, these are budded off from the 

 o-elatinous mass which the coalescence of these prolongations will form on the exterior of the 



* It is remarked by M. D'Orbigny (lxxiii, p. 31) that as the aperture is frequently invisible, 

 not showing itself in above one-sixth of the freshest specimens, the animal may possibly possess the 

 power of closing it. Prof. Williamson (ex) confirms D'Orbigny's statement of the infrequency of 

 the aperture ; but thinks that " its frequent closure is more probably due to the inspissated animal 

 matter of its internal cavity." My own observations satisfy me that the existence of a single 

 aperture of any considerable size is the exception rather than the rule. 



