i^ 



UNITED STATES NATIONAL JVIXTSEUM BTJLLETm 215 



Spherical: Individual chambers forming spheres as 



in Globigerina bulloides d'Orbigny. 

 Clavate: Chambers elongated and may be inflated 



terminally, having a club-shaped appearance as in 



Clavigerinella akersi BoUi, Loebhch, and Tappan. 

 TxjBULOSPiNATE : Chambers produced radially into 



long hoUow extensions, or tubulospines, as in 



Schackoina. 

 Radial elongate: Chambers produced radially as 



ia Rugoglobigerina hantkeninoides Bronnimann. 



Accessory Structures 



These include the structures previously known vari- 

 ously as secondary chambers, chamberlets, umbUical 

 plates, etc., but which are not true chambers as they do 

 not foUow the normal chamber arrangement. They are 

 commonly related directly to the aperture and thus 

 may be considered as apertural modifications (text-fig. 

 4). 



A prominent feature of these accessory structures is 

 that they become progressively more prominent with 

 growth of the test and some are developed only in the 

 adult, so that dissection of the tests fails to show any 

 trace of such features as the bullae of the Catapsydra- 

 cinae. This has been noted before, as F. Parker (1954, 



p. 477), in discussing a species found in the Gulf of 

 Mexico, stated, "Globigerina sp. has a thin supplement- 

 ary chamber extending from the dorsal side between 

 the last-formed chamber and the first one in the last- 

 formed whorl, to varying degrees over the umbihcus. 

 There are supplementary apertures along the sides of 

 this chamber which in many respects is similar to the 

 supplementary chambers of Globigerinita. This cham- 

 ber is apparently resorbed or destroyed when new 

 regular chambers are added since there is no trace of a 

 previous one." 



It is probable that these additional structures serve 

 to protect and reduce the size of primary or secondary 

 apertures. They may also be a weight-increasing 

 development necessary in the adult test to maintain the 

 specific gravity of the animal after the increase to adult 

 test size. The structures thus aid the animal in main- 

 taiaing that depth level in the water where the tempera- 

 ture and water density afforded optimum conditions for 

 the species. Thus, the absence of bullae in younger 

 stages is not surprising. Its presence solely in the adult 

 nevertheless does not lessen its taxonomic value, as 

 many other important characters are developed only in 

 the adult stages of Foraminifera. 



Simple apertural lip: This is the simplest form of 

 apertural modification or cover and may be narrow 



Simple Lateral 



Apertural Lip Apertural Flanges Umbilical Teeth 



Chamber Flanges 



Tegilla 



Umbilical Bull< 



Sutural Bulla Umbilical-sutural Bulla 



Figure 4. — Apertural modifications in planktonic Foraminifera. 



Areal Bulla 



