273 Systematic Paleontology 



The only specimens of this species which have been seen are silicified, 

 and these do not show the internal structure. It is possible that when thin 

 sections are made of calcareous specimens G. macropora may be found to 

 be a species of either Eridotrypa or Batostomella. 



Occurrence. — Helderberg Formation, New Scotland Member. 

 North foot of Moore Knob. 



Collection. — U. S. National Museum. 



Genus ERIDOTRYPA Ulrich 



Eridotrypa parvulipora n. sp. 

 Plate XLIII, Figs. 5-8 ; Plate XLIV, Figs. 7, 8 



Description. — Zoarium consisting of slender, cylindrical ramulets, 

 generally about 2.5 mm. in diameter, increasing to 3 mm. just before 

 bifurcation which occurs at intervals of from 10 to 20 mm. Surface even, 

 the macule of larger cells, which are usually quite inconspicuous, gen- 

 erally including from one to three open interspaces. Zooecial apertures 

 oblique and rather regularly arranged longitudinally in young examples, 

 becoming more direct and polygonal with age, thin walled, 8 to 9 in 2 mm. 

 Acanthopores small, usually seen only in sections and on well-preserved 

 surfaces; irregularly distributed, wanting, apparently, over considerable 

 spaces ; when most abundant, three or four surround a zooecium. Meso- 

 pores few, almost restricted to the macular, always inconspicuous ex- 

 ternally, generally discernible in thin sections only. 



In thin sections the vertical sections show that the zooecial tubes are 

 thin-walled in the axial region, becoming moderately thickened in the 

 short peripheral zone. The diaphragms, one to three, usually two in each 

 tube, are developed only in the bend from the axial to the peripheral 

 regions. None have been observed in the mesopores. The minutely 

 stippled structure of the walls characterizing species of this and related 

 genera is but obscurely shown in tangential sections — probably because of 

 defective preservation. 



This form has all of the characters of the long-lived genus Eridotrypa 

 and is rather closely related to the Trenton types. The zorecia, however, 

 are smaller and the longitudinal arrangement of their apertures more pro- 

 nounced than in any other species having equally large zoaria. 



