120 
MEMOIRS OF TEE QUEENSLAND MUSEUM. 
furrow is well incised and bears a pair of small pits at the anterior angles. The 
occipital ring bears a prominent, narrow, hollow spine. The fixed cheeks, in 
the central region, are slightly more than half as wide as the glabella; the 
palpebral lobes are only slightly curved, medianly situated and are about half 
the length of the cephalon ; the palpebral ridges are very faint, converging on 
the anterior corners of the glabella. The anterior limbs of the facial suture 
are subparallel; the posterior limbs diverge but, near the palpebral lobe, they 
are subparallel to the posterior cephalic margin. 
The pygidium is subtriangular to subcircular in outline. The axis has 
five segments, the posterior segment being semi-circular in outline and, in the 
adult forms, is not prominently marked from 
the one before it. There are five pairs of lateral 
ribs that are well rounded and sharply separated 
by narrow furrows. Oblique furrows on the 
crests of these ribs can faintly be seen on some 
specimens. There are six pairs of hollow, 
marginal spines, five of these are long and 
slender and arise rather abruptly from the 
lateral ribs while the sixth or posterior pair is 
but faintly indicated and is situated axially. 
The four anterior pairs of marginal spines are 
subequal in size ; but the fifth pair is longer and 
thicker. Each spine arises from a rather 
thickened base. The doublure of the pygidium 
is narrow, wire-like, and of uniform width. 
No other parts of the test are known with certainty. 
Remarks : Fragments of this species representing 15 heads and 20 tails 
have been examined. Because of the hollowness of the granules, the ventral 
surface of the test is correspondingly pitted; and on a slightly abraded test the 
dorsal side may appear finely perforate. 
There are a number of species, like D. tenella, in which the fifth pair of 
pygidial spines only are of exceptional size. Of these the most similar forms 
are the genotype D. richthofeni Dames (1883, p. 24, pi. 1, figs. 1-6), D. pergranosa 
Resser and Endo (1937, p. 210, pi. 31, figs. 6-13) and D. matsushitai Resser 
and Endo (1937, p. 210, pi. 43, figs. 22-23). These are the species, all of them 
from China and Manchoukuo, with which comparison is most pertinent. They 
have, also, in common with certain other species, the prominent pair of pits 
at the anterior angles of the cephalic axial furrow. D. richthofeni is easily 
distinguishable by the presence of glabellar furrows and by the coarser ornament. 
D. pergranosa is the most similar species and, indeed, D. tenella is to be 
separated from it only by minor though constant criteria. In general there is 
a most close agreement between these two species in outline, degree of granu- 
lation, type of pygidial spines, and the furrows of the pygidium. D. tenella, 
however, has facial sutures rather more parallel anteriorly, the pygidial spines 
arise a little more abruptly, and the furrow between the two posterior axial 
