34 SYNOPTIC COLLECTION. 



Dendritine variety in which the last chamber is taking the 

 rectilinear mode of growth. Fig. 3 is the Spiroline vari- 

 ety of the same genus in which a considerable portion of 

 the shell is rectilinear. Fig. 4 (Peneroplis arietinus 

 Batsch.), fig. 5 (longitudinal section of the same), and 

 fig. 6 (Peneroplis cylindraceus Lamarck) show the gradual 

 diminution of the spiral portion and the increase of the 

 rectilinear part. These figures illustrate the changes 

 from a spiral to a rectilinear mode of growth in different 

 species of one genus, while the slides No. 24 (specimens 

 obtained from the sand of the Bahamas) and PI. 25, figs. 

 1-5, exhibit the changes from a spiral to an annular growth 

 in one species, OrbicuJina adunca F. u. M. PL 25, fig. 6, 

 is a section giving the interior of the shell. It shows that 

 the primordial chamber was globular and that subse- 

 quently spiral growth took place followed by annular 

 growth. 



Unusual interest attaches to the species Orbitolites ten- 

 uissima Carpenter (PI. 26). Beginning as a globular 

 shell it passes into the undivided Cornuspira condition 

 which is clearly marked in the young; the later convolu- 

 tions are sometimes constricted at opposite points, thus 

 indicating the Milioline stage. Next the spiral stretches, 

 after the fashion of a Peneroplis. The chambers extend 

 themselves extraordinarily in breadth, until by the meeting 

 of the lateral ends a ring is formed around the spiral part 

 of the shell, as in Orbiculina. These annular rings or 

 chambers are divided by cross walls into a great number 

 of chamberlets. Finally the complex structure with many 

 additional covering cells or chambers peculiar to Orbito- 

 lites is developed. 1 



Miliola, Peneroplis, Orbiculina, and Orbitolites belong 

 to the calcareous group of Porcellanous Foraminifera. 

 The calcareous group with a hyaline or glassy appear- 



1 For further information see Carpenter, Rep. Chall. Exped., 

 Zool., VII, part XXI, 1883, pp. 1-49, pis. I-VIII. 



