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XII. — Note on the Large Size of the Spicules of Acis orientalis. 



By F. Jeffrey Bell, M.A., Sec. K.M.S. 



{Bead lith November, 1888.) 



In the year 1882, Mr. Stuart 0. Eidley described * a species of Acis 

 from Mauritius. A specimen lately purchased by the Trustees of the 

 British Museum from the same island shows that the examples seen hy 

 Mr. Eidley were either starved or incompletely grown. In the very 

 much finer example lately acquired the spicules of the coenenchym are 

 seen to form quite a stout armour for the colony, and the examination 

 of it leads to a few considerations of some interest. The scales may 

 be as much as 7 mm. long. These large plates appear to he 

 scattered quite irregularly over the colony ; that is to say they are not 

 more common on one side than the other, on the larger than the 

 smaller branches; they are not more frequently developed at the angles 

 of branching than elsewhere ; they are quite irregular in form, but 

 they are always longer than broad, and there is a tendency to a 

 lozenge-shape. The smallest plates may not be more than about half 

 a millimetre along their longest axis, but these are, of course, visible to 

 the naked eye ; between these two extremes there are plates of every 

 possible intermediate size. 



The plates of the calicles offer a somewhat remarkable disposition ; 

 they are arranged in two or three rows of shghtly imbricating scales of 

 varying size ; often, though not always, the basal scales are larger than 

 those above them ; the mouth of the cup is guarded by eight scales, so 

 small as to be only just visible to the unaided eye. These scales 

 exhibit a simplified arrangement of the type which Professor KoUiker 

 has made familiar to us by his figures of Primnoa lejxidifera, 

 P. verticillaris, and P. regularis. A somewhat similar, but simpler, 

 striation is seen on the scales of the cortex of the ccenenchym, but the 

 larger plates are almost smooth, and exhibit no characteristic markings. 

 The indentations at the edges, where they unite with their "neighbours, 

 offer nothing worthy of notice. 



It appears to be obvious that the point of real interest in this 

 species is the remarkable size of the cortical scales ; other forms have, 

 before now, been described as having large scales, such as Thesea exserta 

 or Acis guaclalupensis, but the greatest length given by KoUiker for 

 the former is 1 • 2 mm., and for the latter 2 • mm. In CahjfAroij'wra 

 jai^onica Dr. Grray reports that the scales are large, but the largest 

 scales, which are not those of the coenenchym but of the polyps, are 

 not more than 1 mm. in their greatest length. The interest of 'this 

 large size of the spicules lies in the fact that palfeontologists, with the 

 exception of Pocta,t seem to have hitherto neglected to look for the 

 deposits of Alcyonarians on account of their small size ; or, as Prof. 



* Ann. and Mag. Xat. Hist., x. (1882) p. 126. 

 t See SB. K. Akad. Wiss. Wien, xcii. (1885) p. 7. 



