ART. 25 GENERA SIPHOGENEKINA AND PAVONINA CUSHMAN 3 



Both microspheric and megalospheric forms occur in the various 

 species of this genus. In the microspheric form the early chambers 

 are biserial or triserial, and there is usually a considerable number of 

 them before the adult uniserial development takes place. In the 

 megalospheric form the uniserial condition is taken on much earlier, 

 after only a few of the triserial or biserial chambers are developed. 



In the present ocean the species are found in the Indo-Pacific most 

 abundantly, but also in the Western Atlantic and the Mediterranean. 

 In the fossil condition the genus occurs in the Tertiary as noted under 

 the various species. 



Halkyard in his paper edited by Heron- Allen and Earland ^ places 

 Siphogenerina as a subgenus of Bigenerina. The relationships, how- 

 ever, seen to be with Uvigerina and the Lagenidae. In microspheric 

 specimens of Siphogenerina bifrons the early chambers sometimes 

 show a decidedly coiled character, linking the early development of 

 Siphogenerina with coiled forms Uke that of Cristellaria. 



A rough key is given to the species of the genus treated here: 



A KEY TO THE SPECIES OF SIPHOGENERINA 



Test not compressed: 

 Costate — 



Costae few and prominent — 



Costae more prominent than suture lines — 



Test large and fusiform S. collomi 



Test tapering throughout — 

 Costae high, lamellate — 



Costae 10 or less S. raphanus 



Costae 15 or more S. reedi 



Costae, low, not lamellate S. kleinpelli 



Costae less prominent than suture lines S. branneri 



Costae numerous and prominent — 



Neck short S. striata, var. curta 



Neck long and slender S. irregularis 



Costae very numerous, not prominent S. striatula 



Lamellate — 



Lamellae very prominent, not spinose S lamellata 



Lamellae less prominent, spinose near base S. spinosa 



Smooth — 



Test slender and elongate S. columellaris 



Test short and stout S. hughes! 



Coarsely punctate S. dimorpha 



Spinose"or hispid S. virgula 



Slender, early portion costate, middle spinose, later part smooth _S. mexicana 

 Test compressed: 



Short, stout, sides deeply depressed S. bifrons 



Elongate,^slender, sides not depressed S. advena 



• Mem. Proc. Manchester Lit. Philos. Soc, vol. 62, pt. 2, 1919. p. 37. 



