666 PALEONTOLOGY OF/ ILLINOIS. 



Rhombopora, the principal difference is found in the more or 

 less numerous pores which (normally) are situated back of the 

 zooecia apertures. 



The Devonian species of the genus Hall has placed under his 

 new genus Acanthoclema. They are, however, quite distinct 

 from his A. alternation, which is mentioned as the type, and 

 which is closely related to Rhombopora. 



STREBLOTRYPA MAJOR Ulrich. 



PI. LXXI, fig. 8-8d. and PI. LXXII, fig. l,la. 



Zoarium a comparatively robust, dichotomously or otherwise 

 dividing stem. Often found flattened from pressure. The divi- 

 sions of the branches occur at long intervals and are often 

 unequal. Zooecia apertures oval, 0.25 mm. long and about 0.15 

 mm. wide, surrounded by a narrow sloping area, only notice- 

 able in perfect specimens; arranged in longitudinal series (inter- 

 rupted at more or less frequent intervals) between subangular 

 longitudinal ridges, that are not distinct from the aperture 

 margins but form their lateral boundaries. The longitudinal in- 

 terspaces between the succeeding zocecia apertures exhibit the 

 mouths of from one to three short ranges of mesopores. These 

 pores vary considerably in size, and in number from three to 

 twelve, but when the zooecial arrangement is regular, their num- 

 ber is generally either four or six. Measuring longitudinally, 

 about ten zocecia apertures occur in 5 mm. 



Of internal characters, the comparative shortness of the zoce- 

 cial tubes, the non-development of an inferior hemiseptum, and 

 the rather irregular appearance of the tubes in the axial region, 

 are the most noteworthy. 



The large zocecia and rather robust zoarium easily distinguish 

 this species from all others of the genus so far known. 



Position and locality: Keokuk group; King's Mountain, Ky.; 

 Keokuk, Iowa; Nauvoo and other localities in Illinois. The 

 specimens from Illinois are larger than those from Kentucky. 



