MARYLAND GEOLOGICAL SURVEY 293 



HORMOTOMA GRACILENS (Whitfield) 



Plate XXXV, Figs. 4, 5 



Murchisonia gracilens Whitfleld, 1889, Bull. Amer. Mus. Nat. Hist, vol. ii, 

 p. 53, pi. viii, figs. 14, 15. 



Description. Shell rather small, possibly reaching 25 mm. in length, 

 and very slender with the apical angle not more than 16 to 18 degrees, 

 consisting of numerous whorls, six of which occur in the upper part of the 

 spire of a small individual in 6 mm. Volutions ventricose, smooth or 

 with but a very slight angularity near the middle of the exposed portion ; 

 sutures deep and strongly marked. Columella and aperture unknown. 



This species is probably the Canadian representative of the abundant 

 Middle and Upper Ordovician Hormotoma gracilis Hall which it greatly 

 resembles. The earlier species, however, is a trifle more slender. 



Occurrence. BEEKMANTOWN LIMESTONE (Turritoma zone). Stouf- 

 ferstown, Pennsylvania, and near Huyett, Maryland. 



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



Genus TURRITOMA Ulrich 

 TURRITOMA ACREA (Billings) 



Plate XXXV, Fig. 11 



Murchisonia acrea Billings, 1865, Pal. Foss., vol. i, Geol. Surv. Canada, 

 p. 232, text fig. 216. 



Description. Shell rather small and slender, about 25 mm. long and 

 7 mm. at its widest portion, resembling a Turritella; apical angle 15 to 

 20 ; whorls 12 to 15 in number, flat or subconcave, each with the lower 

 edge angularly rounded and projecting slightly over the one below; 

 surface above this projection flat or gently concave; and sloping to the 

 suture, near which is a slight convexity. Surface characters unknown. 



This shell is easily recognized even in poor specimens by its consider- 

 able resemblance to a small species of Turritella. Its characters are so 

 distinctive that Ulrich selected it as the type of his genus Turritoma. 



