AMMODISCOIDES, A NEW GENUS OF AEENACEOUS 

 FOKAMINIFERA. 



By Joseph A. Cushman, 



Of the Boston Hocivtii of Natural Hifitor]/. 



While examining the original material upon which Dr. Axel Goes 

 based his paper on the Foraminifera of the expedition to the Gala- 

 pagos Islands, a few species included in that report from the Gulf of 

 Mexico were studied. Among these, certain specimens were found 

 under the name of AmmocUscus incertus d'Orbigny, which were at 

 once seen to be peculiar. Instead of the ordinary piano-spiral test of 

 that species these specimens were found to^be really conical, especially 

 the young, the first few revolutions forming a hollow cone. This por- 

 tion stands out as a large prominence in the younger specimens, espe- 

 cially when seen in the view shown in fig. 3, An illustration of this 

 young alone is shown in fig. 4. In later growth the revolutions form 

 a low, flaring cone in the reverse direction. This character may be 

 best seen in the diagrammatic sections, figs. 5 and 6. In occasional 

 specimens, instead of reversing the direction, the cone developed in 

 the young simply becomes more flaring. The specimens were all from 

 the Gulf of Mexico, from Albatross Station 2383, from 1,181 fathoms. 

 In all there were eighteen specimens of varying size. The specimens 

 from the Pacific in the Goes collection were all of the typical Ammo- 

 discus tenuis or A. incertus forms, all piano-spiral throughout their 

 development. 



In the early development of the conical species there is a certain 

 resemblance to Gordiaminna and Turritellella^ but the later portion 

 is very different. Each of the eighteen specimens had a micros]:)heric 

 proloculum, or initial chamber. The early coils are very uniform in 

 size, and in this respect are again like the other two genera to which 

 reference has already been made. In texture the specimens are much 



Proceedings U. S. National Museum, Vol. XXXVl— No. 1676. 



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