Maryland Geological Survey 397 



Spirifer perlamellosus Hall 

 Plate LXIX, Figs. 4-6 



Spirifer perlamellosa Hall, 1857, Tenth Ann. Rept. N. Y. State Cab. Nat. 



Hist., p. 57, figs. 1, 2 (marked erroneously Spirifer ventricosa = Nucleo- 



spira ventricosa) . 

 Spirifer perlamellosus Hall, 1859, Nat. Hist. N. Y., Pal., vol. iii, p. 201, pi. 



xxvi, figs. la-Is, 2a-2g, 1861. 



Description. — " Shell trigonal or semicircular, more or less extended on 

 the hinge-line, the extremities varying from obtuse or rounded to ex- 

 tremely mucronate. Ventral valve arcuate, the beak much extended be- 

 yond the opposite valve, and incurved at the apex; sinus deep, gradually 

 expanding, and produced in front into a linguiform extension. Dorsal 

 valve convex toward the middle, the mesial elevation very prominent, and 

 the beak closely incurved against the area, or partially closing the foramen 

 of the ventral valve. Area moderately wide, frequently much expanded, 

 and becoming linear towards the extremities where the shell is much 

 extended. 



" Surface marked by from four to six strong and ahruptly elevated 

 plications on each side of the mesial sinus and elevation, concentrically 

 marked by strong imbricating lamells, which are abruptly arched in 

 passing over the plications, giving an extreme roughness to the surface. 

 In well-preserved specimens, finer longitudinal lines mark the surface of 

 these lamella;. In ordinary specimens the concentric lamellae are more 

 closely arranged and more distinctly imbricate towards the margin ; while 

 near the beaks they are more distant, and are scarcely imbricate." Hall, 

 1857. 



Length 1.7 cm. ; width 3 cm. 



In Maryland this well-known and widely distributed Helderberg 

 brachiopod is abundant, but rarely attains the size of New York specimens. 

 The plications, as a rule, are somewhat fewer in number, often are far 

 more abruptly elevated, and vary in JSTew York specimens from four to six, 

 while in Maryland material there are from three to five. Again, in the 

 southern specimens, the ventral cardinal area is more bent backward, 

 while in the northern individuals it is more often vertical and relatively 

 higher. A few localities only are cited in the following paragraph : 



