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Show 274 DR. J. S. BOWERBANK ON L^P1'' 6> I am indebted to my late friend Mr. Henry Deane for two specimens of this interesting species ; neither of them exceeds 8 lines in height and 5 in greatest diameter. From their form and other external characters they might readily have been mistaken for specimens of Farrea gassioti; but a microscopical examination readily separates them from that species. As was the case with F. gassioti, the characters derivable from the dermis, oscula, and pores were not available ; so that the discrimination of the species was in a great measure dependent on the structural peculiarities of the skeleton ; and the resemblance of the two species in size, form, and mode of arrangement of the spicula is very close; but they differ very strikingly in the characters afforded by the central canals of the skeleton- structure. In those of P. gassioti, when examined beneath the microscope in Canada balsam with a power of 108 linear, they are strikingly large and distinct, while in F. pocillum, although the fibres of the two species are as nearly as possible of the same size, they are remarkably slender, and in some cases nearly obsolete ; and this was the case iu portions taken from both of the specimens in my possession. These distinctive characters are quite sufficient to separate the two species ; but there are fortunately others that aid materially in their discrimination. Thus in F. pocillum there are numerous internal defensive organs of a rectangular sexradiate form, based on the sides of the skeleton, and projected into the areas of the rete. These organs are comparatively large and strong, and are abundantly furnished with large conical spines. Sometimes the primary central portion of these organs is destitute of the four lateral radii; and occasionally the lateral radii are doubled in number, a second set of them being projected beyond the first ones. In addition to these internal defensive organs there are numerous unattached rectangular sexradiate spicula, occasionally grouped together in considerable numbers on the areas of the skeleton-rete. These spicula are very distinct from those organs of the same form which are based upon the skeleton-fibre ; they are very much smaller, and their radii are slender and usually spineless. All are alike acutely terminated, and have evidently never been based upon the skeleton-fibres, as the organs first described always are. The presence of these organs in the one species and their apparent complete absence in the other strongly confirms the propriety of their separation, notwithstanding the close resemblance they bear to each other in external form. The specimens were dredged July 22, 1872, in lat. 14° 8' N., long. 77° 38' W., 800 to 1000 fathoms, by Capt. Hunter, R.N. DEANEA, Bowerbank. Skeleton siliceo-fibrous. Fibres canaliculated ; canals continuous. Rete symmetrical ; areas rotulate, confluent. This genus is intermediate between Iphiteon of Valenciennes and Farrea. The skeleton has the confluent rotulate structure of the former, but differs from it in having the fibres distinctly canaliculated. It agrees with the latter genus in the canaliculation of the |