MARYLAND GEOLOGICAL SURVEY 193 



Description. This species forms small, sub-globular masses, from 

 one to two inches in diameter. The concentric lamellae are thin and 

 closely packed together, there being in some specimens from 6 to 12 layers 

 in the thickness of two lines. 



The internal structure is described by Dr. Nicholson as follows: 

 " Composed of radiating capillary tubes, arranged in concentric strata. 

 The tubes vary from 1/12 to 1/20 mm. in size, and are in direct contact 

 throughout, no interstitial tissue of any kind being developed. The tubes 

 are irregular in form, with thin often undulated walls, which are not 

 pierced by any apertures or pores, but are often crossed by more or fewer 

 transverse partitions of ( tabulae/ Very commonly the tubes exhibit 

 more or fewer inwardly directed partitions, which extend to a greater or 

 less distance into the cavity of the tube, and are the result of the cleavage 

 or ' fission ' of the tubes." 



An intensive study of this wide-spread and long-ranged fossil will in all 

 probability reveal the fact that a number of distinct species are included 

 under the name Solenopora compacta. 



Occurrence. CHAMBERSBURG LIMESTONE (Caryocystites bed). Fort 

 London and localities south to Blue Spring, Franklin County, Pennsyl- 

 vania. A wide-spread and abundant fossil in almost all of the divisions 

 of the Middle and Upper Ordovician in North America. 



Collections. Maryland Geological Survey, TJ. S. National Museum. 



SPONGIAE ? (CALCAREOUS ALGAE ?) 



Genus NIDILITES Salter 

 NIDULITES PYRIFORMIS Bassler. i 



Plate XLVI, Figs. 1-5 



Nidulites sp. Bassler, 1909, Bull. Virginia Geol. Surv., vol. iia, pi. vii, fig. 11. 

 Nidulites pyriformis Bassler, 1915, Bull. U. S. Nat. Mus., no. xcii, p. 855. 



Description. The body of this interesting organism, which is such an 

 abundant fossil at certain horizons in the Chambersburg limestone of 

 the Appalachian Valley, is pyriform and pedunculate, with an outer 



