49 
DESCRIPTION OF A NEW SPECIES OF POROCRINUS, 
FROM THE TRENTON LIMESTONE. 
With remarks on the Genus, by JAMES GRANT, M.D.; F.R.C.S.; F.G_S., ete. 
Genus Porocrinos, BILLINGS. 
Porocrinus, Billings, Report Geological Survey of Canada, 1856. 
Porocrinus, Billings, Decade 3, Geological Survey of Canada, 1859. 
Porocrinus, Meek and Worthen, Proc. Acad. Nat. Sci. Phila., 1865. 
This genus was founded on one species from the Trenton Limestone at 
Ottawa :—P. Conicus, the type of the genus. In the Proceedings of the Academy 
of Natural Sciences, Philadelphia, 1865, Meek and Worthen described P. Pentago- 
nus, from the Trenton Limestone, and P. Crassus from the Hudson River Group, 
both from Illinois. 
We have now a new species from the Trenton Limestone at Belleville, dis- 
covered by Mr. W. R. Smith, of that city. 
The specimens examined exhibit some new features, which do not, however, 
in any way invalidate the original description of the genus. 
In the original description of P. Conicus the pores are spoken of as “ fine 
elongated parallel slits which appear to penetrate through the plates.” In the 
descriptions of P. Pentagonus and P. Crassus the divisions between the pores are 
mentioned as “ plates.” A careful examination of the new specimens, about to 
be described, show that the pores do not open on the outside surface, each pair of 
plates being externally arched, making the hydrospires appear like one side of a 
collection of flat black tubes placed side by side, while one specimen (Fig. 2) has 
on several of the hydrospires a thin investing membrane, as in Paleocystitis and 
Comarocystitis. E. Billings states that in these last named genera it is probable that 
the pores are not visible externally unless the surface is worn. I fancy that all 
the species of Porocrinus already founded were described from worn specimens. 
The membrane mentioned covers each hydrospire completely and obliterates the 
sutures of the plates where it covers them. 
I cannot find that the vault plates or the structure of the arms have been 
before observed. Meek and Worthen, in describing P. Crassus, state that the vault 
seems to consist of three or four comparatively large plates.” The vault and 
arms described hereinafter are much the same as in Cyathocrinus (as revised by 
Wachsmuth. ) 
Porocrinus, SMITHI, Sp. Nov. 
Basals.—-Five, pentagonal, wider than high, of nearly equal size. 
Subradials.—Five ; three hexagonal and two heptagonal. 
Radials.—One by five, as long as the sub-radials, while four of them are 
wider, hexegonal, excepting that their apices are notched about one-fifth the 
length of the plates to form a part of the passages of the arms, and in two of 
them the angle adjacent to the proboscis is wanting. Articulating facets about 
one-quarter the width of the radials, and extending downwards nearly to their 
centres. 
Brachials.—One- by five, as wide as arm joints, but at their points of 
greatest length nearly three times as long as an arm joint. 
Azygos plates two, the lower one quadrangular, resting on the two hepta- 
Hee plates ; and the other, pentagonal, supported on one heptagonal and the 
ower azygos plate. 
