MARYLAND GEOLOGICAL SURVEY 203 



Description. " Rhabdosome very small (9 mm. mostly less) and 

 slender (1-1.3 mm. wide), elliptic in section, widening gradually, possess- 

 ing a gently wavy median furrow on each lateral face. Sicula small 

 (1.3 mm.) and very slender, provided with a short apertural spine; its 

 slender virgella protruding from the rhabdosome. Thecae tubular, little 

 inclined to the axis of the rhabdosome in the proximal half and sub- 

 parallel to it in the distal free half; closely arranged (12-14 in the space 

 of 10 mm. or 32 in 1 inch) ; apertures straight, at right angles to longer 

 axes of thecae. Nemacaulus thin." Euedemann, 1908. 



A common species of the Ohio and Mississippi valleys, New York, 

 Canada, etc., ranging from t*he Trenton to the Richmond. 



Occurrence. MARTINSBURG SHALE (Corynoides bed). Chambers- 

 burg, Pennsylvania, and Williamsport, Maryland. 



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



CLIMACOGRAPTUS SPINIFER (Ruedemann) 

 Plate LIT, Figs. 3, 4 



Climacograptus typicalis mut. spinifer Ruedemann, 1908, New York State 

 Mus. Mem., vol. xi, pt. 2, pp. 411, 412, pi. xxviii, figs. 8, 9, text fig. 236. 



Climacograptus spiniferus Ruedemann, 1912, New York State Mus., Bull. 

 162, p. 84. 



Description. This species is distinguished from the well-known Cli- 

 macograptus typicalis Hall, which it most closely resembles, in the 

 presence of two straight, thin spaces and in the closer arrangement of the 

 thecae, the majority of the specimens having 14 thecae in 10 mm. In the 

 presence of the two spines this species resembles Climacograptus bicornis 

 Hall, but in the latter species these spines grew from the first two thecae 

 and are not prolongations of the sicular spines as in C. spinifer. 



Occurrence. MARTINSBURG SHALE (Corynoides bed). Chambers- 

 burg, Pennsylvania, and Williamsport, Maryland. Trenton shale of 

 eastern New York. 



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



