DESCRIPTION OF SPECIES 319 



tions, the first eight of wliich are formed by bifurcation of four plications. 

 The i^lications outside of the first eight do Jiot bifurcate. The mesial fold 

 originates at the beak and is set off from the rest of the shell by grooves 

 that are deeper and wider than those between the plications. The fold 

 is narrow and elevated near the front margin of the shell. Two plications 

 on the fold originate at the beak and each subdivides into three or four 

 before reaching the front margin. 



MARTINIA n. sp. 

 Plate 19, figures 17-18 



The collection contains a single example of a shell that agrees^ in gen- 

 eral, with the genus Martinia. Its dimensions are : Length, 9.5 milli- 

 meters; breadth, 6.6 millimeters; greatest thickness, which is in the 

 umbonal region, 4.5 millimeters. Absence of growth lines suggests an 

 immature shell. Compared with the Mississippi Valley species, M. . con- 

 tracta and M. sulcata, the most striking difference is the greater length 

 over breadth. 



PUGNOIDES OTTUMWA (White) 

 Plate 18, fi.?ures 12-14 



1862. Rhy7ichonella ottumwa White, Proceedings of Boston Society of Natural 



^History, volume 9, page 23. 

 1914. Pugnoides ottumwa Weller, Illinois Geological Survey, monograph 1. 



pages 193-195, plate 25, figures 7-17. 

 1916. Pugnoides ottumwa Weller, Contributions from Walker Museum, volume 



1, number 10, page 246, plate XVI, figures 7-8. 



This species is common, but most of the specimens are not well pre- 

 served. It agrees with Welter's description, but seems to average a little 

 narrower compared to the length. The means of the measurements of 

 seven typical specimens are: Length, 11 millimeters; breadth, 11.2 milli- 

 meters; thickness, 6.2 millimeters. A yomig specimen, 8 millimeters 

 long, 8 millimeters wide, and 4 millimeters thick, has no plications on the 

 fold and in the sinus and has incipient plications on the margins. 



C0MP08ITA TRINUCLEA (HaU) 



Plate 18, figures 1-4, 9 



1856. Tcrchratula trhniclcus Hall, Transactions of Albany Institute, volume 4. 



page 7. 

 1914. Composita trinuclca Weller, Illinois State Geological Survey, monograph 



1, page 486, plate 81, figures 16-45. 

 1916. Composita trunclea Weller, Contributions from Walker Museum, volume 



1, number 10, page 246, plate XYI, figures 3-6. 



