AND DISTRIBUTION OF TRILOBITES, 271 
in one specimen I counted twenty-two ; in all the species nearest 
related to it, with which I am acquainted, the number is cer- 
tainly smaller, but always exceeds eleven. In Ph. macrophthal- 
mus and in other species considered as belonging to the Caly- 
mene, on the other hand, I always found their number below 
eleven, but I never met with the joints of the axis distinctly 
visible to the most extreme point of the axis, as is the case in 
A. Hausmani. Taking these distinguishing characters as a basis, 
I for the present divide Phacops into two subgenera, leaving it 
to be decided whether they do not merit the rank of independent 
genera for further researches. 
A. Phacops in the restricted sense (Calymene, Brong. in part). 
Contractile. Fins rounded at the extremity, with an acutely 
sharpened anterior margin. Caudal axis furnished with 11 
or fewer joints. 
Ph. macrophthalmus, Brong., protuberans, Dalm., crypto- 
phthalmus, m. (Calymene levis, Miinst.?), sclerops, Dalm. 
(Powisii, Murch.), conophthalmus, Boeck, Downingie, Murch. 
(PL. IV. fig. 2.), proavius, m (Pl. IV. fig. 3.), rotundifrons, m. 
B. Dalmania (Asaphus, Brong. in part, Asaphus, Goldf.). Not 
contractile : fins at the anterior margin scarcely sharpened, 
frequently acute.- Forehead always clavate, distinctly lobed. 
* Caudal shield furnished with more than 11 , Sometimes with 
as many as 22 joints of the axis, frequently elongated at 
the extremity of the tail. 
Ph. caudatus, Brinn, mucronatus, Brong., Hausmanni, 
Brong. (PI! IV. fig. 1.), odontocephalus, Green (Pl. IV. fig. 4.), 
truncato-caudatus, Portl. 
II. Phillipsia, Portl. Facial suture extending to the posterior 
margin. Forehead almost cylindrical. Thorax 9- to 10- 
jointed.—Carboniferous formation. 
a. Nine-jointed species: Phacops Kellii, Jonesii, ornata 
(Pl. IV. fig.7.), and other species discovered by Portlock 
in the Irish mountain limestone. The facial suture 
is not yet known in all the species considered as be- 
longing to this group. 
b. Ten-jointed species: Asaphus Dalmani, Goldf., from 
the Carboniferous limestone of Ratingen. Differs from 
Phacops (with which Professor Goldfuss has recently 
united it) in the number of thoracic rings and facial 
suture. 
ee 
