1896. ] NEW YORK ACADEMY OF SCIENCES. 231 
Size.—‘ Length and width of the shields, 34 mm. 
Horizon and Locality.—Fine dark shales of Div. 1 d! (the 
highest layers) at Porter’s Brook, St. Martin’s. 
The Latin description contains no reference to the thorax; 
this is described in the next paragraph (Swedish). ‘‘ First joint 
of the thorax somewhat smaller than the second, rachis with 
two tubercles at the sides; the pleure of the first joint are di- 
vided into a larger front tubercle and a smaller back tubercle by 
a furrow ; the tubercles on the pleurz of the posterior joint are 
of about the same size. 
Var. TRIFIssus n. var. Plate xvi., fig. 10. 
This is about the same size as the type, and is distinguished 
by two additional furrows at the front of glabella, one at each 
corner, beside the median furrow that characterizes the type; 
these furrows cut into the cheeks in front of the glabella; the 
median furrow is the longest, but none connect with the anterior 
marginal furrow (or the median one, rarely). There are two 
minute tubercles at the axial line of the first lobe of the rachis 
of the pygidium. 
Horizon and Locality.—In the Davidis Subzone at Chapel 
Arm, Trinity Bay, Newfoundland. Also in the Abenacus Sub- 
zone (Div. 1 d!) at Porter’s Brook, St. Martin’s, N. B. 
Development of the Young.—At the } mm. stage (14 mm. for 
the complete animal) the head shield already shows the cleft 
fore-lobe of the glabella, and a shallow indentation across the 
glabella marking off the first somite of the posterior lobe; the 
basal lobes are scarcely yet visible. The thorax has’ only one 
joint; this joint has tubercles on the sides of the rachis and a 
furrow on the pleura running directly outward; no pleural tu- 
bercles. The rachis of the pygidium is not lobed, but the so- 
mites are indicated by the incipient keel of the second lobe, and 
avery minute tubercle near the front of the third lobe, indicating 
the third somite; at the front of the rachis isa strong transverse 
ridge, the “ half joint ” (articulating ridge) more prominent now 
than in later stages. The first somite of the pygidium is not 
yet visible, but it is separated in the 14 mm. stage (24 mm. for 
the whole animal ), when the rachis divides into three lobes. 
Only one joint of the thorax of this stage has been seen; it shows 
tubercles on the pleurz as well as on the rachis. When the 
animal becomes 3 to 34 mm. long both joints appear in the thorax 
and the general features of the test are those of the adult ; the 
basal lobes of the head shield are still very small. 
These features of growth in 4d. fissus are based on examples 
