267 



[Smith. 



Thus the finding of Pronorites in Arkansas is of great importance, 

 since it is tlie ancestor of a form Medlieottia, which tliougli unknown 

 in Arkansas, has been found at no great distance away in the Texas Per- 

 mian.* Pronorites, on the otlier liand, lias not yet been found in Texas. 



These occurrences lielp to prove the continuity of life from the Car- 

 boniferous into the Permian, and to show that the same conditions 

 existed here as in the Artinsk region of the Ural mountains, where the 

 Carboniferoiis beds contain the goniatites out of which most of the Per- 

 mian ammonites were developed. 



Pronorites <\i/rlolotjus Phillips, variety arkiinsiensis J. P. Smith, PI. xxiv, 

 Figs. 1—4. Oonidtites cydolobus Phillips, Geol. Yorkshire, Vol. ii, 

 p. 237, PI. XX, Figs. 40^2. Goniatites cydolobus Phillips, Verneul, 

 Geol. Russia and the Ural Mountains, Vol. ii, p. 370, PL xxvi, Fig. 4. 

 Goniatites cydolobus Phillips, Roemer, Palceontographica, ix, p. 

 167, PI. xxvii, Fig. 1. Goniatites cydolobus Phillips, DeKoninck, 

 Faune calc. Carh. Belcj., Vol. ii, p. 121, PI. 1, Figs. 5, 6. Pronorites 

 cydolobus Phillips, (variety tiralensis) Karpinskj', Mem. Acad. Iin- 

 per. Set. St. Petersbourg, vii series. Tome 37, No. 2, p. 8, PI. i. Fig. 4. 



Phillips' original description of Goniatites cydolobus is as follows : 

 "Discoid, sides flat, back broad, inner whorls half concealed, septa 

 with four round lateral lobes, a small double dorsal lobe, and small 

 acute dorsal sinuses, the first lateral sinus double, the others simple, all 

 round." 



This description is too meagre to be of more than generic value, and 

 also the term "dorsal " is used where now "abdominal " is in common 

 use. 



The shell is smooth, discoidal, very involute. The sides are nearly 

 parallel and the breadth increases very slowly ; the abdominal shoul- 

 ders are nearly square, and the abdomen flat. The whorls are deeply 

 embracing and increase rapidly in height. The umbilical shoulders are 

 square, the umbilicus narrovr and deep, and increases slowly in diame- 

 ter. 



Dimensions. — The specimen, Avhich was septate throughout, gave the 

 following dimensions : 



MM 



Diameter 34.0 



Height of last whorl from umbilical shoulders 17.5 



Breadth 10.0 



Width of umbilicus 7.0 



This gives the proportions: 1: 0.5: 0.29: 0.20 : which agree almost 

 exactly with Karpinsky's figures, 1 : 0.5 : 0.30 : 0.20. On the Arkansas 

 specimen the involution is shown by the height of the last whorl from 

 the top of the next inner one, 12.5 mm. as compared with ihe total 



*C. A. White, Bull. 71 U. S. Geol. Survey, p. 21. 



