388 OHIO BIOLOGICAL SURVEY 



G- Median part transversely 



oval 31. T. schauinslandii 



E-' Posterior spike-like process longer 



than diameter of shell . . 32. T. ensifera 

 A2 Surface of shell provided with distinct spines. 



Bi Spines not uniformly distributed over entire sur- 

 face. 



C^ Posterior spines absent. ... 33. T. acanthostoma 



C^ Posterior spines present. 



D^ Spines in a single row on posterior or 



posterior and anterior end . . 34. T. armata 

 D- Spines covering entire shell except an 



equatorial belt . ... 35. T. raciborskii 



B^ Spines uniformly distributed over entire surface. 

 C^ Form spherical or nearly spherical. 



Di Posterior part of shell not produced into 

 a spike-like process. 

 El Spines short and numerous. 



Fi Form spherical, covered with 



prominent short but distinct 



spines. . . . . 36. T. globularis 



F- Form oval, largest anteriorly, 



covered thickly with fine minute 



spines . . . . 37. T. westii 



E- Spines extremely long, equal in length 



to diameter of shell, about 10 in 



number 38. T. americana 



D- Posterior part of shell produced into a 



spiike like process . . . 39. T. aegyptraca 



C- Form not spherical, the length approximately 

 twice the diameter. 



D^ Posterior part of shell not produced into 

 a spine like process. 



El Form regularly oval, neither the ante- 

 rior nor the posterior end broadest. 

 F^ Anterior end developed into a 

 neck like process ... 40. T. piscatoris 

 F- Anterior end broadly rounded. 



G^ Granulations between spines 

 absent. 



H' Spines as long as or 

 longer than length of 

 shell ... 41. T. setosa 

 H- Spines short. 



V Spines bent . 42. T. spinosa 

 I- Spines straight. 



Ji Posterior end 



broadly rounded 43. T. hispida 



