Schuchert — Jackson on the Phytogeny of the Echini. 263 



clearly evinced, by the structure and development of the 

 ambulacra, an entirely new method of getting ontogenetic 

 stages of growth (231). 



Lepidesthidm (Lepidechinus, Perischodomus, Perischocidaris, 

 Proterocidaris, Lepidesthes, Pholidocidaris, Meekechinus), " one 

 of the most specialized of ah groups of Echini," with 2 to 20 

 columns of ambulacrals and 3 to 13 of interambulacrals, plates 

 imbricating and no resorption of base of corona, priinaryspines 

 small ; Devonian to Permian. 



Order Echinocystoida (new), arose in the same stock that 

 gave rise to Perischoechinoida but is an offshoot from a com- 

 mon early stock. Irregular in form witli the periproct appar- 

 ently eccentric in an interambulacrum. From 2 to 1 columns 

 of ambulacrals and 8 to 9 of interambulacrals. Plates thin 

 and imbricating, with the spines small. Lantern typically echi- 

 noid, but no perignathic girdle. Families Palaeodiscidge (Palae- 

 odiscus) and Echinocystidse (Echinocystites). 



Art. XXIY. — The Belt and Pelona Series; by Oscar H. 



Hershey. 



The sedimentary rocks of the Coeur d'Alene Mountains in 

 Northern Idaho were first systematically studied in 1903 and 

 1904 by Mr. F. C. Calkins, assisted by Messrs. W. A. Williams 

 and D. F. MacDonald.* Although consisting chiefly of 

 variable proportions of only two minerals, quartz and sericite, 

 it was found practicable to subdivide them into six formations 

 as in the following table : 



Generalized Tabular Section in Coeur d^Alene District. 



Approximate 

 Name Description thickness 



in feet 



Striped Sandstones, siliceous, generally flaggy to shaly; 

 Peak color mostly green .and purple : characterized 

 by shallow-water features, as ripple marks, 

 sun cracks, etc. Top removed by erosion. 1,000 -f 



Wallace Thin-bedded, bluish and greenish, more or less 

 calcareous shales, underlain by rapidly alter- 

 nating thin beds of aigillite, calcareous 

 sandstone, impure limestone ; these under- 

 lain in turn by gray-green siliceous argillites. 

 Ripple murks, sun cracks, etc., throughout. 4,000 



*The Geology and Ore Deposits of the Coeur d'Alene District, Idaho; 

 Prof. Paper U. S. Geol. Survey No. 62, 1908. 



