MICRO FA UNA FROM JOHNSON COUNTY, ILLINOIS 



83 



Texas and the Mud Springs Mountains in 

 central New Mexico. Later, Thompson 

 (1944, p. 420) discovered the genotype 

 species, M. marblensis, in the Brentwood 

 limestone at the well-known type section 

 of the Morrow group in northwestern 

 Arkansas, and defined the zone of Millerella 

 as that part of the stratigraphic section con- 

 taining this fusuline to the exclusion of the 

 normal long-axis forms. He also stated that 



It is entirely possible, if not probable, that spe- 

 cies of Millerella or of a closely allied ancestral 

 genus of fusulinids will be found in rocks of Mis- 

 sissippian age. 



Later (1945, p. 42) he stated that 



All fusulinids so far discovered in the Belden 

 formation (Idaho) are referable to the genus Mil- 

 lerella, which was originally described from the 

 upper part of the Marble Falls limestone of 

 Texas. Congeneric species are known to occur 

 stratigraphically from near the base of the Mor- 

 rowan series to near the top of the Pennsylvanian 

 system. It is probable that further study will 

 demonstrate the occurrence of Millerella in rocks 

 older than Morrowan. 



Endothyra has long been considered by 

 some as the progenitor of the fusulinids 

 (Galloway, 1933, pp. 388, 393; Dunbar and 

 Henbest, 1942, p. 52) but most fusuline 

 students have considered that the true 

 Fusulinidae were confined to the Penn- 



sylvanian and Permian. However, the 

 recognition of Millerella in zones of the 

 upper Chester in the type area demonstrates 

 conclusively the occurrence of true fusulines 

 in Mississippian rocks as Thompson pre- 

 dicted. 



The thin sections of Chester Millerella 

 were shown to Dr. Thompson at the Pitts- 

 burgh meeting of the Geological Society of 

 America, and they were later sent to him for 

 direct comparison with his described mate- 

 rial. He states that "I have compared the 

 specimens you sent me with all other similar 

 forms I have in the laboratory. So far as I 

 can tell they are more closely similar to the 

 types of Millerella inflecta from the Belden 

 formation of northwest Colorado." 1 



There are, however, some important and 

 easily recognized differences between the 

 Chester forms (pi. 19, figs. 1-12) and those 

 previously described (pi. 19, figs. 13-18), con- 

 sequently the older forms are described as 

 new species. These distinguishing features 

 are as follows: 



1. The very strongly rounded periphery. 



2. The relatively short, straight septa rapidly 

 widening near the outer wall and producing a 

 structure which is A-shaped in cross section 

 (see sagittal sections), in contrast to the thin, 



1 Personal communication, January 27, 1946 



Explanation of Plate 20 



Figs. 1-3 — Prioniodus scitulus Branson and Mehl. Lateral views, X20. (p. 92) 



4-10 — Cavusgnathus cristata Branson and Mehl. Oral, aboral, and lateral views; 4-6, 8-10, X20; 

 7, X30. (p. 91) 



11-13— Hindeodella sp. Lateral views; 11, X20; 12, 13, X30. (p. 91) 



14-16 — Taphrognathus varians Branson and Mehl. Oral, lateral and aboral views, X30. (p. 92) 

 17 — Ligonodina cf. L. levis Branson and Mehl. Lateral view, X30. (p. 91) 



18 — Glomospira disca Cooper, n. sp. Lateral view of holotype, X60. (p. 87) 



19-23 — Endothyra excentralis Cooper, n. sp. 19, 21, Lateral views and 20, aperatural view of a 

 young specimen; 22, lateral view of holotype showing involute right side and greatly en- 

 larged final chamber; 23, apertural view of holotype. X60. (p. 88) 

 24, 30 — Endothyra acuta Cooper, n. sp. Lateral views, X60. 24, Holotype, showing umbilicus, 

 depressed sutures, and sharply curved outer margin of chambers, bed 5. 30, Smaller speci- 

 men showing highly arched aperture, bed 4. (p. 88) 

 25-27 — Hyper ammina cf. elongata clavulata Howchin. Lateral views of three fragmentary speci- 

 mens, X60. (p. 88) 

 28, 29 — Hyper ammina sp. Lateral views, X60. (p. 89) 

 31, 32 — Palaeotextularia asper Cooper, n. sp. Lateral views, X60. 31, Holotype. (p. 89) 

 33 — Hyperammina cf . H. glabra Cushman and Waters. Lateral view of a nearly complete speci- 

 men, with initial chamber, X50. (p. 89) 

 34-41 — Trepeilopsis mississippiana Cooper, n. sp., Lateral views, X60. 36, 39, 41, Specimens 

 showing tube bent back over earlier whorls; 38, specimen coiled about a Productus spine; 

 37, regular coils without development of straight portion. 34, 35, from bed 1 ; 36, 38, 40, 41, 

 beds 5, 6; 37, bed 7; and 39, bed 4. 40, 41, Two views of the holotype, showing wide, flaring 

 aperture. 34, 35, Two views of a single specimen. (p. 87) 



