274 bulletin: museum of comparative zoology. 



from the boulders at Rysedorph Hill was described from an incom- 

 plete cephalon, so that detailed comparison is not possible. It would 

 appear, however, that our species has a narrower fringe and less 

 prominent glabella than specimens from the New York. 



T rinuclcus fimhriatus Murchison, the type of the genus as restricted, 

 is very similar to T. acervulosus, but differs in having more pits in the 

 fringe, particularly at the genal angles. T. fimhriatus is probably 

 from about the same horizon (Llandeilo) as our species. 



Horizon and Locality: — Numerous specimens have been collected 

 by Prof. Roy Holdon from the Athens shale three miles northeast of 

 Blacksburg, Va. Holotype M. C. Z. 1,592. 



Dionideidae, fam. nov. 



Dionideae Giirich, Centrabl. min. geol. pal., 1907, p. 135 {nomen 

 nudum) . 



Dionide has usually been placed with Trinucleus and Ampyx in the 

 Trinucleidae. The structure is, however, not in accord with either 

 of those genera and since they have been separated, Dionide can not 

 logically be placed in either family. The free cheeks are ventral like 

 those of the Trinucleidae but the cephalon does not have a regularly 

 pitted brim and the pygidium is very large. The family may be diag- 

 nosed as follows : — 



Isopygous hypoparia with six segments in the thorax and both shields large. 

 Free cheeks ventral except for the genal spines. Surface of cephalon irregu- 

 larly pitted. Hypostoma short, rounded, tuberculated. 



One genus, Dionide, Barrande. Ordovician, Europe and North 

 America. 



Dionide holdoni, sp. nov. 



Animal of medimn size for the genus; test oval in outUne, about one fifth 

 longer than wide. 



Cephalon short, about three times as broad as long. Glabella relatively 

 short, reaching only two thirds the length of the cephalon, moderately convex 

 in outline, smooth except for the small median tubercle and a larger spine- 

 base back of it. At the sides of the glabella there are faint indentations 

 of a pair of lateral furrows, and at the back is a pair of short longitudinal ones. 

 These latter are somewhat longer in young specimens than in the adults. 

 Fixed cheeks depressed convex, covered with a fine network of irregular radi- 



