MINERALS AND GEOLOGY OF CANADA. 515 
cystites, Comarocystites, Amygdalocystites, Malocystites, Paleocystites, and 
Ateleocystites. The genus Pleurocystites is a very remarkable one. It ig 
chiefly characterised by the dissimilar structure of the two sides of the body; a 
series of comparatively large plates covering the dorsal side, whilst the ventral 
side consists of an open space protected by an integument covered with numer- 
ous small plates. The genus, with us, appears to range from the Chazy to thé 
Hudson River group; and geographically from Canada to Wales and Bohe- 
mia (Caradoc group and Barrande’s étage D.) Six species are enumerated: P. 
sguamosus (plates plane or slightly concave; pectinated rhombs, with obtuse 
angle above); P. robustus? (plates concave); P. filitextus (pectinated rhombs' 
with acute angle above; plates on ventral side fewer and larger than in P. 
sguamosus); P. elegans; P. exornatus ; and P. Anticostiensis (plates probably 
smooth). P. elegans and P. ornatus may perhaps prove eventually to be mere 
varieties of P. filitertus. The genus Glyptocystites is characterised chiefly by 
its cylindrical body, enclosed in four series of plates (= 4 basal + 5 + 5 + 5) 
some with re-entering angles; and by the presence of ten or more pectinated 
rhombs, a strikingly peculiar character. It ranges from the Chazy to the Trenton 
group, and comprises the following species: G. multiporus (arms 4+ 1, ex- 
tending down the sides of the body); G. Logani (plates with stellar ridges, 
arms not developed: Trenton): G. gracilis; G. Forbesi (plates large and 
strong, with numerous ridges and strie: Chazy). Of the genus Comarocystites 
only one species, C. punctatus, has been recognised. It occurs in the Trenton 
group, and may be readily distinguished by its deeply-concave plates. The 
basal plates are three in number, succeeded by from eight to eleven irregular 
rows; the mouth is provided with a valvular apparatus, and there are free arms. 
The genus Amygdalocystites possesses the same plate-formula as Comarocystites, 
and the mouth is also furnished with a valvular apparatus ; but, in addition to other 
distinguishing characters, the arms are recumbent, and composed of a double in 
place of a single series of joints. Three species are enumerated. One of these, 
however, may belong to a distinct genus, and the other two may perhaps be 
united. They comprise: A. florealis, A. tenuistriatus (?), and A. radiatus. In 
both Comarocystites and Amygdalocystites the plates are without pores, at least 
on the unworn external surface. The genus Malocystites has likewise an in- 
definite number of non-poriferous plates.* The arms are recumbent, and the 
mouth is nearly at the apex of the cup. Two species are described: J. Mur- 
chisoni, with eight long and winding arms, and M. Barrandi, with two short 
arms. In the genus named Paleocystites, the plates are numerous and also 
poriferous, or rather crypto-poriferous, as the pores do not extend directly to the 
outer surface, but communicate with the interior through the sutures, on the edges 
of which they open. Nothing is known respecting the arms, orifices, and stem. 
Three species are enumerated : P. tenuwiradiatus,t P. Dawsoni, and P, Chapmani, 
* As subsequently shown, however, by Mr. Billings, the pores in Comarocystites appear 
to open out on the sides of the plates at the sutures, as in the genus Palzocystites. May 
not this be the case, also, with regard to Cryptocrinus (Vou Buch), and the other so-called 
non-poriferous types ? 
+ This is the Actinocrinus tenuiradiatus of Hall. The other species appertaining to the 
different genera enumerated in the text, belong eutirely to Mr, Billings. 
