53b YORKSHIRE TYPE AMMONITES May 



53. AMMONITES TRIVIALIS, Bean MS. (Simpson) 

 (Plate LIII) 



Original Description 

 " 10. A[inmonites] trivialis. [M. Simpson, 1843, pp. 10, ri.] 



[" I. Without a dorsal keel or furrow. 

 " a. No spines." p. 7.] 



" Depressed ; volutions 5, exposed, outer whorl ^ the diameter ; 

 radii numerous, sharp, slender, diverging, form obtuse angles on the back ; 

 aperture subquadrate, widest near the back ; diameter | inch. 



"This Ijeautiful little ammonite is from the lowest beds of lias. 

 It has been named by my friend Mr. Bean, to whom it has been [p. 11] 

 long known. Like several others from these beds, it is of a fine bronze 

 colour. This together with the elegance of the whorls and radii, render 

 it one of the most beautiful of our ammonites. On the inner whorls 

 the radii are very close, and on the outer whorls, they are gradually more 

 and more separated by flatfish spaces ; the aperture becomes more and 

 more quadrate, and the radii, before passing over the back, form small 

 tubercles. Different individuals vary considerably both in the breadth 

 of the outer whorl, and in the prominence of the radii. On some, the 

 radii are strong and prominent, others have the outer whorl nearly 

 smooth." 



Additional Details 



Simpson, 1855, p. 44, — Omits " Depressed " and " aperture sub- 

 quadrate, widest near the back," in first par. Omits 2nd sentence of 

 2nd par., and last sentence but one. Adds to last sentence " indeed 

 the Varieties are so numerous, that they can scarcely be defined." 



Simpson, 1884, y^, 74, — p. 74 reads in first sentence of 2nd par. 

 " from the Lower Lias ", and at end says " L.L., x, R.H. Bay, Saltburn." 



Remarks 



There are three specimens numbered 105 in Whitby Museum register 

 marked as Simpson's types. Of these the specimen now depicted in 

 Fig. I agrees best with the original description, and may be considered 

 to be the holotype ; the other two being paratypes. 



Stages, Fig. i, periphery, 2, 2c to ic : ornament 3 to 5 ; Fig. 2, 

 periphery 2 ; ornament 3 to 5 commencing — development disturbed by 

 injury ; Fig. 3, periphery, 2 ; ornament 3, 3c to 2c — temporary cata- 

 genesis ? All have conch serpenticone. 



Genus, Polymorphites, Sutner in Haug, 1887 ; family, Polymorphidae, 

 Haug. The geological position given by Simpson is where the jamesoni 

 is in contact with the valdani zone : the same position is given by Haug, 

 1887, 117 (P. polymorphus). Figs. 2 and 3 are referable to forms named 

 by Quenstedt and d'Orbigny, as noted below. 



Result 



1. Polymorphites trivialis, Bean-Simpson sp. 1843 ; 



2. Polymorphites mixtus, Quenstedt sp. 1846 ; 



3. Polymorphites jupiter, d'Orbigny sp. 1850 ; 

 Charmouthian, valdani zone, Robin Hood's Bay, near Whitby. 



