20 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 95 



generic characteristics, three rays curved to the left and two to the 

 right. Smaller, young examples, such as the type itself, have rays 

 less curved, and in still younger specimens the rays are almost straight. 

 A view of the specimen on the type slab showing the anal pyramid 

 well preserved is represented on plate 7, figure 12, where the rays, 

 although almost straight, show a tendency to curve left and right as 

 in the older examples. The other characters of the genus are those of 

 typical Isorophus. Typical Agelacrinitcs has the same arrangement of 

 arms as in Isorophnsella, but its sculptured mosaic interambulacral 

 plates will readily distinguish it. 



LEPIDODISCUS Meek and Worthen, 1868 



Theca with the curvature of the ambulacra as in Discocystis, 

 namely, four rays to the left and one to the right, but differing in the 

 presence of strongly imbricating interambulacral plates. Or again, 

 the genus resembles Cooperidiscus except that four of its ambulacra 

 curve to the left instead of five to the right. In addition to L. (^Agela- 

 crinites) squanwsus (Meek and Worthen), the genotype, (pi. i, 

 fig. 17), L. (Agelacrinites) beecheri (Clarke), L. (Agelacrinites) 

 buttsi (Clarke) (pi. 7, fig. 8), L. (Agelacrinites) lebouri (Sladen) 

 (pi. I, fig. 19), and L. milleri Sharman and Newton (pi. 7, fig. 7), 

 all from the Lower Carboniferous rocks, exhibit the curvature of 

 ambulacra and imbricating interambulacrals characteristic of the 

 genus. The following new species from the Middle Devonian is thus 

 the earliest known. 



LEPIDODISCUS ALPENENSIS, n. sp. 



Plate 3, fig. 3 



The type and only specimen, a theca about 7 mm in diameter, at- 

 tached to a large Chonetes, shows clearly four ambulacra curved to 

 the left and the fifth, the right posterior, to the right, as well as the 

 strongly imbricating plates of typical Lepidodisciis. The anal pyra- 

 mid, although somewhat broken, is large and occupies a central posi- 

 tion between the left and right posterior rays. The small size and the 

 combination of characters diagnostic of the genus will separate this 

 species from other Devonian edrioasteroids. 



Occurrence. — Devonian (Traverse group-Presque Island division 

 of Long Lake formation), Quarry of the Alpena Portland Cement 

 Company, Alpena County, Michigan. 



//o/o/'v/'^'.— Collection Geological Department, University of Michi- 

 gan, no. 17296. 



