394 Mr. VV. N. Lockington on the Porcellanidea of the tubercles and their interspaces iiniformly finely porous. No oscula, and no distinct canal-sjsteni. Corpuscles small, consisting of a thickened centre from which six to eight, smooth, straight, or slightly curved arms issue. The union of these arms, either with the nodes or arms of neighbouring corpuscles, produces a hexactinelliform lattice-work (PI. VIII. fig. 5). The whole of the original specimen is set with spicules and isolated siliceous corpuscles, only a portion of which probably belongs to Mastosia. Geodia-\x\ie. spherules are the most abundant. There are also large and small bacillar spicules, pointed at one or both ends, small cylindrical spicules with rounded ends, simple quadriradiates with smooth and spiny arms, spicules with a short shaft and sliort forked anchors. This remarkable new genus is known only from the pas-sage-beds of the White Jura e and ^ at Sozenhausen, near Giinzburg, where it was obtained by M. Wetzler. The largest specimens attain a diameter of nearly 2 decims. The species is named Mastosia Wetzleri. [To be continued.] XLIV. — Bemarks ujyon the Porcellanidea of the West Coast of North America. By W. N. LOCKINGTON. The accompanying list of Porcellanidea (which includes de-scriptions of nine species I believe to be new, since they are certainly distinct from any of those described or mentioned by Stimpson as found upon this coast) does not profess to be complete, but merely to give facts of distribution and other particulars respecting forms with which I am acquainted. Stimpson, in his ' Prodr. des Anim. ^vert.' 1858, divides the old genus Porcellana into the following genera : — Petro-listhes, Pisosoma, Paj^hidopus, Pachycheles^ Megalohrachium^ Porcellana^ Minyocerus, Porcellanella (White) , and Polyonyx. In the first two of these the first joint of the antennal base is short, not reaching the margin of the carapax ; while in all the others the first joint is more or less produced, and joined to the margin of the carapax. The more convex carapax, stouter chelipeds, and less pro-jecting front are the characters which separate Pisosoma from Petrolisthes] but as some of my species have some of the cha-racters of the former genus, while they are without others^ I find it exceedingly difficult to discriminate. I have therefore included Pisosoma in Petrolisthes, placing the former name in brackets before the specific names of such species as, in my
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