8 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
ActinoLosus Eichwald, 1860. 
Type, InLaENnus atTavus Eichwald, 1857. ‘ 
Lethaea Rossica, 1860, 1, p. 1488. 
The type is an illaenid which seems sufficiently peculiar to deserve 
a distinct genericname. 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 
atavus 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 [llaenus mascket (From F, Estland). : 
PanpvDERIA 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 writer 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. 
