310 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxxv. 



thick, bulb-like form of the posterior lobe, which single swelling 

 comprises both the median and the posterior lobe of a true Beyrichia, 

 and by its surface ornament. The second group consists of species 

 without surface ornamentation and whose average size is inferior to 

 that of the first group. The posterior lobe is smaller and commonly 

 exhibits a tendency to segregate a small node or undefined swelling 

 on its inner slope that doubtless represents the larger and more 

 definitely separated median lobe of Beyrichia. 80 far this section 

 is known by seven Ordovician species, one Silurian, one Devonian, 

 and one early Mississippian species. It seems probable that the two 

 Ordovician forms described by Krause as Bollia minor and Bollia 

 major* are also referable to this section. They are most certainly 

 not true Bollias. 



As now restricted and defined. Ctenobolhina includes the following 

 species : 



group of ctexobolbixa ciliata. 



ORDOVICIAN SPECIES. 



CtenobolMna alata h Ulrica. 

 Ctenobolhina bispinosa b Ulrich. 



'" ■" ,,,,, v »».^L». 



CtenobolMna ciliat<i h {Beyrichia ciliata Emmons). 



CtenobolMna curta b (Ctenobolhina ciUata, var. curta Ulrica). 



CtenobolMna duryi b {Beyrichia duryi Miller). 



CtenobolMna emaciata h {CtenobolMna ciliata, var. emaciata tlricli). 



Ctenobolhina guillieri {Beyrichia guillieri Tromelin). 



CtenobolMna hammelli 1 {Beyrichia hammelli Miller and Faber). 



CtenobolMna obliqua h Ulrich. 



Ctenobolhina oblonga {Entomis oblonga Steusloff). 



SILURIAN SPECIES. 



CtenobolMna granosa h Ulrich. 

 CtenobolMna punctata b Ulrich. 



DEVONIAN SPECIES. 



CtenobolMna papillosa h Ulrich. 



GROUP OF CTENOBOLBINA SUBrRAKSA. 



ORDOVICIAX SPECIES. 



Ctenobolhina crassa '' Ulrich. 



CtenobolMna fulcrata h Ulrich. 



Ctenobolbma impressa {Entomis impressa Steusloff). 



CtenobolMna major {Bollia maj or Krause). 



CtenobolMna minor {Bollia minor Krause). 



CtenobolMna subcrassa h Ulrich. 



CtenobolMna umbonata^ {Entomis umbonata Steusloff). 



"Zeits. .1. «l. geol. Gesell., XLIV, is<»i>, ]>]>. 391, 392, pi. xxi, figs. L5, is. 

 b American species. 



