ORDER III 



TREPOSTOMATA 



337 



Rhombotrypa U. and B. Silurian. Petalotrypa and Jlixmfrjijm Ulr. Ordovician 

 to Devonian. 



Family 6. Halloporidae Basnler {Galloporidae Ulricli). 



Zoaria ramose, sub-frondescent, massive or discoidal. Zocecial apertihres generally 

 sub-circular and separated more or less completely by angular mesopores ; at other times 

 polygonal, ivlien the mesopores are few or wanting. Zoacial tubes thin-ivalled, attaining 

 tlu'ir fall size slowly. Aranthopores wanting. Ordovician to Devonian. 



In this lainily the proximal ends of the tubes arising in the axial or "immature" region 

 have the character of mesopores. The diaphragms are rather closely arranged in the tapering 



7? 



iisy/^" 



•a,^ o 



Fic. 49U. 



Hallopora ramosa (E. and H.). Ordovician (Cincinnati Group); Cincinnati, Ohio. .1, Zoarium, natural 

 size. B, Surface slightly magnified. (', Tangential section, parallel to external surface, ""/j. D, \'ertical 

 section, 20/j. (c'and D after Nicholson.) 



proximal end, then few or wanting for a considerable distance, and finally become crowded in 

 the peripheral or mature region. 



Hallopora Bassler {CaUopora Hall preoccupied) (Figs. 490, 491). Zoaria usually 

 ramose and liusliy, the brandies often anastomosing. Ai^ertui'es closed in tlie perfect 

 state by perforated, often ornamented, covers, wliicli are left behind, as growth proceeds, 



Fic. 491. 



A, B, Hallopora eU(jantula(Ji.&\\). Niagara; Indiana. Vertical and tangential sections, w/j. C, D, H.multi- 

 tabuluta Ulr. Lower Trenton ; Minnesota. C, Vertical section, "/i. D, Surface having zocecia open (7/j), and 

 preserving zocecial covers (i*/i). 



to form floors (diaphragms) of succeeding layers. Zooecial tubes of two sizes in the axial 

 region, the larger ones with six to eight sides, the smaller set four- or five-sided. 

 Ordovician to Devonian. 



Halloporina, nom. nov. (proposed for Calloporina Ulrich and Bassler, preoccupied 

 by Neviani in 1895). Like Hallopora but diaphragms wanting and walls strongly 

 crenulated. Ordovician. 



Calloporella Ulr. Silurian ; North America. 

 VOL. I Z 



