590 Systematic Palko.xtology — Uppeu Devoxian 



geologic position. Following Schvichert in eschewing the term aspcra as 

 not applicable to our Devonian species the writer includes under one term 

 the Chemung species which have been generally known as .1. aspcra and 

 A. liystrix, the latter presenting the spinous senile or genetic condition 

 of the former in the same manner as the Hamilton species A. spinosa 

 shows a like but much more accelcraicd conditinn of a more finely ribl)ed 

 Atrypa. 



In the broad sense, therefore, the term lu/strix is applied to these large 

 rough-shelled Atrypas of the [Maryland Chemung. Shells with highly 

 convex dorsal valves, very shallow ventral valves, bearing seldom more 

 than 8-10 plications with sometimes only 3 or 5 obscure ones visible. 

 Among the concentric frills on the surface of these shells occasionally a 

 single fold forms a spine, or a given frill a row of such infolded tubular 

 extensions, though none seem to have attained great length. The rela- 

 tion of these shells to those of Atrypa reticularis is seen upon comparison 

 of the early growth stages of the two. The sparsely ribbed infantile or 

 nepionic condition of A. reticularis is continued throughout the life of 

 A. liystrix, which in this respect is an instance of arrested development, 

 while in company with this life-long, infantile condition is the attainment 

 of great size, and the early manifestation of such senile traits as the ex- 

 cessive exiidation of test substance in the form of excrescences. \\'ii\\ 

 reference tlien to ..4. reticularis, A. liystrix is an overgrown and senile 

 infant, the degenerate offshoot of an expiring race. 



Length 30 mm.; width 35 mm. 



This species is restricted to higher horizons while .1. spinosa is more 

 usual at lower horizons. 



Occurrence. — Jennings Formation, Chemung Member. Xational 

 Road west of Frostburg; Oakland- Altamont Eoad ; Oakland-Redhouse 

 Koad ; Trout Bun 2 miles south of Oakland ; on the road from Oakland to 

 Deer Park; in the vicinity of Cherry Creek and of Deer Park Station; 

 in the railroad cut at Altamont; Allegany Grove, 2315; Ellerslie, Penn- 

 sylvania, 131() ; Town Creek 47GS) ; at many outcrops in the Polish Moun- 

 tain sections along the National and the Williams roads; one-half mile 

 east of Millstone Point; and just west of Tonoloway Hill. 



Collection. — Maryland Geological Survey. 



