MINUTE STRUCTURE OF STROMATOPORA AND ITS ALLIES. 245 



absence of the so-called vertical " radial pillars " are conspicuous 

 characters. 



Fig. 10. Sketch of a limited portion of another vertical section of S. canaclcnsc, 

 examined with a 4-inch objective (= X 10 [diam.). In this a large 

 vacuity surrounded by granular matter is prominent. 



Plate IV. 



Fig. 1. Pachi/stro7ym sp.? Portion of the exterior undulating surface, of 

 natural size, showing the superficial star-shaped depressions or "radiate 

 water-canals." 



Fig. 2. TacJiystroma antiqua, Nich. & Murie. View of a small part of a larger 

 specimen, of nat. size, exhibiting the wavy layers as seen in the ex- 

 posed weathered condition. From the Upper Silurian (Niagara 

 Limestone), Canada. 



Fig. 3. A polished vertical section of a piece of P. antiqua, of nat. size, showing 

 the contorted thick lamina?. 



Fig. 4. A transparent microscopical specimen, being a vertical section of P. 



antiqua, about twice nat. size. In this the interlaminar structure is 

 rather indefinite. 



Fig. 5. A transverse or slightly tangential section of P. antiqua, also X 2 diam. 



The circular area appears to correspond to the nodular eminences 

 (possibly stellate systems) of the exterior crust, and in some respects 

 bear a partial likeness to the columns of Stylodictyon columnar e, though 

 by far larger. What the artist has represented in dark doited lines 

 and broken inner circle are under the microscope apparently sarcode- 

 chambers, on the whole rather indistinct. 



Fig. 6. Tachy stroma {Syringostroma) densa, Nich. A vertical transparent 

 section, x2 diam. The sinuous layers in two places enclose sandy 

 concretionary substance. The laminaj are relatively shallow and the 

 small-sized chambers somewhat indefinite. From the Corniferous 

 Limestone (Devonian), Ohio. 



Fig. 7. View of a small portion of a tangential section of P. densa, under a 

 2-inch objective ( = X20 diam,). 



Fig. 8. A vertical transparent section of what appears to be a Stromatoporoid 

 from the Trenton Limestone, Canada, and here represented of twice 

 nat. size. There is a marked series of horizontal or concentric 

 laminae of average or considerable thickness. What appears to answer 

 to vertical pillars are thin, linear, occasionally tubular-like threads, 

 passing from one to two or more laminae, and here and there joining 

 each other so as to form oblong cells ( = ? sarcode chambers), these 

 being filled throughout by crystalline matter. There are besides what 

 correspond to columnar areas, which pass vertically upwards and 

 seem formed of obliquely meeting cell (?) boundaries. The indefinite 

 nature of this specimen makes us hesitate to describe it until further 

 examination be instituted. 



Fig. 9. A polished median vertical section of portion of another undetermined 

 Stromatoporoid from the Cincinnati formation (Lower Silurian), 

 Wajmesville, Ohio. Drawn of nat. size, and placed in the Plate cross- 

 wise to what may have been its natural position — that is, it may origi- 



