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XIX. — Notes on Phoronis hippocrepia. By F. D. Dyster, Esq., F.L.S. 



Read July 1st, 1858. 



idLAVING recently had an opportunity of examining the very remarkable creature, first 

 described ])y Dr. Wright* under the above appellation, I was desu-ous of contriljuting 

 some details, with respect to its structure, in addition to those contained in that author's 

 observations. 



The colony on which my observations were made appeared in a tank, on a small piece of 

 hard limestone which had been in the aquarium for a considerable time (I believe, some 

 months), and which, covered with Serpulce and other tubicular Annelids, and Actinice, was 

 clearly derived from between tide-marks. To the naked eye, the Phoronis presents very 

 much the appearance of Cycloum, but is rather more robust in build. The animals grow 

 closely aggregated together, each individual inhal)iting a tul)e buried in holes in the rock, 

 but which does not project beyond its surface, and is consideralily larger than the body : 

 the tube is membranous and flexible, and appears to be formed by the incorporation of 

 mud with an exudation furnished by the worm. In coloiu- they present the silvery white- 

 ness of the Polyzoa. They differ greatly in size, varjang from -^§i\v to iT^ths of an inch in 

 length (when fuUy protruded), of which length the tentacula make about ^th ; the breadth 

 of the body is from Tooth to s'g-rd of an inch, and the spread of the tentacula from i-g-th 

 to i^ths of an inch. The body is cylindrical, slightly flattened on the haemal surface, and 

 semitransparent, presenting no trace of somites, annulations, setse, or uncini. Trimcate 

 obliquely forwards and backwards, with a slight dilatation at the summit, it is crowned with 

 a double row of tentacles springing from the two margins of a horseshoe-shaped lophophore, 

 round the rami of Avhich they are continued, recalling most vi^ddly the cephalic apparatus 

 of the hijipocrepian Polyzoa. The outer row of tentacles spread into a cup, while the inner 

 row arch towards each other, covering the space between the arms of the horseshoe, inter- 

 lacing at their tips, and forming a cradle for the ova ; the tentacles arc filiform, silvery 

 white, varying in number from 16 to 86, and united for a short distance from their bases by 

 a delicate membrane. The motions of the tentacles are individually voluntary, and some- 

 what sluggish. The creature itself is timid ; and the slightest touch, or any jar commu- 

 nicated to the water, causes it to withdraw with great activity : but the tips of the tenta- 

 cles always protrude from the tube. The whole body is in constant gentle swaying mo- 

 tion, and is capable of considerable extension as well as protrusion. The animals are 

 provided with great power of reproducing lost parts. An abstracted head is renewed 

 within 48 hours, not completely developed, but with a serviceable mouth and its covering 

 valve and stumpy tentacles which do their work of providing food. The tentacles are 



* Edinburgh New Philosophical Journal, vol. vii. p. 313, tab. vii. 

 VOL. XXII. 2 L 



