Notes on Spirifera Parryana. 23 



Walcott cites a reference to this species, which 1 have not 

 seen — namely, an article by Billings, 1861, Canadian Journal, 

 Vol. VI, page 261, Figs. 77, 78. 



Spirifera parryana is enumerated m the list of Devonian 

 fossils from Rock Island county, Illinois, Geological Survey of 

 Ilhnois, Vol. V, page 222. 



Spirije7'a ■parryana, like very many other organic forms, 

 varies within somewhat wide Hmits. The variation, however, 

 is not greater than in Spirifera poinata, Owen, or any other 

 species that occurs at a number of widely separated localities. 

 There are differences in size depending on differences in age, 

 but even adult individuals differ greatly in this respect. The 

 largest specimen before me, and the largest of the species S. 

 parryana I have seen anywhere, has, measured in inches, the 

 following dimensions, — length 1.60, width 2.35, thickness 1.48. 

 Between this extreme and immature specimens only a fraction 

 of an inch in their greatest measurement there are all possible 

 gradations. Perhaps the most obvious variations are those 

 that concern the relative proportions of length, width and 

 thickness. There are thick forms with short hinge and 

 rounded cardinal angles at one extreme, and relatively thin 

 forms with extended hinge and acute cardinal angles at the 

 other. At one extreme the thickness, length and width are 

 approximately equal; at the other, the length is one and 

 one-half and the width two and one-ninth times the thickness. 

 The average form it would seem has not yet been illustrated. 

 Hall's and Owen's figures are all short-hinged forms. The 

 figures of Meek and Worthen, Geological Survey of Illinois, 

 Vol. Ill, page 433, Plate XIII, Fig. 8 a-b, described as S. 

 /ornacula. Hall, more nearly represent the average individual 

 of S. parryana than any other so. far published. 



The width of the hinge area along the hinge line, in an 

 extremely globose form, is but little more than twice the 

 height. In average specimens the width is three and three- 

 fourths to four times the height, but in one instance before me 

 the width is fully seven times the height. The area may vary 



