8 bulletin: museum of comparative zoology. 



AcTiNOLOBUS Eichwald, 1860. 



Type, Illaenus atavus Eichwald, 1857. 



Lethaea Rossica, 1860, 1, p. 1488. 



The type is an illaenid which seems sufficiently peculiar to deserve 

 a distinct generic name. The cephalon is short and the pygidium long, 

 and both cephalon and pygidium have a-concave border; the cephalon 

 a narrow lip, and the pygidium as wide a border as the average Isotelus. 

 The eyes are rather large, far back and far apart, free cheeks small, 

 genal angles rounded. The dorsal furrows of the cephalon are short, 

 the axial lobe of the thorax is narrow; ten segments are present; and 

 the axial lobe of the pygidium is short and triangular. Actinolobus 

 ataviis is a Russian Ordovician species (Cla), and another species with 

 a wide border on the pygidium is the one from the Silurian described 

 by Schmidt as Illaenus masckei (From F, Estland). 



Panderia Volborth, 1863. 



Type, Panderia triquetra Volborth. 



Mem. Acad. imp. sci. St. Petersburg, 1863, 6, no. 2, p. 31. 



Although proposing this name primarily to replace the preoccupied 

 Rhodope of Angelin, Volborth made his own new species the type, 

 and the genus must rest upon it. Holm does not actually use 

 Panderia, but he seems to have considered it a fit receptacle for the 

 group of small trilobites with only eight thoracic segments, and gives 

 (1883, p. 161) a new definition according to his interpretation of the 

 genus. The presence of only eight segments in the thorax does not 

 appeal very strongly to the present WTiter as a generic characteristic. 

 Panderia triquetra does, however, present some rather unusual charac- 

 teristics in its very short, strongly convex cephalon with extremely 

 large eyes, the high, well-defined glabella, and the short pygidium 

 with long, prominent axial lobe. Species of this type are not at all 

 common, and may be referred to Illaenus without doing violence to 

 the definition of that genus. 



