uc^ 



Annals ok the Carxe(;ie Museum. 



Neanic Stages. — As in S. miicfonatiis diWd Cy?-tina liamiltonensis the 

 first change from the nepionic shell is the formation of a ventral sinus, 

 which is bounded by two strong ridges. This is followed by the for- 

 mation of a fold and two plications on the dorsal valve. Plications are 

 then introduced, in pairs, on the lateral margins. \Vith the appearance 



Fk;. 49. Spirifer crispus ( Hisingei"). Dorsal and cardinal views of a specimen 

 from ^\'aldron, Ind. X 2. Compare with Fig. 48. 



of the first pair of plications the hinge width becomes greater than the 

 width below and, during the later stages, the shells are mucronate. 

 The index varies from 1.13 in a shell .44 mm. long with 4 plications, 

 to 2.30 in a shell 6 mm. long and bearing 12 plications. The 

 adults have from 10 to 14 strong plications. Unfortunately, the 

 deltidial plates are so completely broken away in all the specimens 

 as to make it impossible to learn anything of their manner of devel- 

 opment. 



It is interesting to note that these transversely elongated Devonian 

 Spirifers pass through, in their early neanic stages, forms which cor- 

 respond to the adult condition of 

 certain Niagara species. The adult 

 of 6". crispus, with a fold and eight 

 plications on the dorsal valve, the 

 ventral valve deeper than the dor- 

 sal, and a hinge width nearly equal 

 to the width below, corresponds 

 very closely in these particulars, and 

 in its index, with a specimen of ^. 

 mucroriatiis about 2 mm. long and, 



Fig. 50. The same species. Dorsal 

 and cardinal views of a specimen from 

 Gotland. X 4- 



Figs. 49 and 50 are from specimens 

 in the Baron de Bayet collection, now 

 the property of the Carnegie Museum. 



except in the number of plications, with a specimen oi D. consobriuus 

 one mm. long (Figs. 49, 50). 



Spirifer radiatiis, with no plications, the width only one seventh 

 greater than the length, and the width at the hinge less than the width 

 below, corresponds to a still earlier stage in the development of these 

 species. 



