282 Dr. \\\ C Mcintosh on the Boring ofcertam Annelids. 



chalk and limestone, the empty perforations, however, do ex- 

 hibit a form somewhat like a keyhole in transverse section ; 

 but in the calcareous rocks and stones containing living speci- 

 mens the double tube is completed by an intervening column 

 of debris, except at the loop. In not a few of the worn pieces 

 of chalk and limestone, only the widened inferior end or junc- 

 tion of the tube remains. This is a point of some interest, 

 since Dodecaceria concharum abounds in the same sites, and its 

 gallery is distinguished in transverse section by having no in- 

 curvation, or only a very slight incurvation in the middle, and 

 is not double ; yet the dried remains of this worm might most 

 aptly be described " as a black carbonaceous film," whereas the 

 dried remnants oi Leucodore are of a pale or straw-yellow hue. 



Amongst the minute fragments of flint which form the 

 fine gravel of Luccomb Chine, in the Isle of Wight, are 

 many loose rounded pieces of limestone and chalk more or 

 less perforated by Leucodore and Dodecaceria ; but the living 

 examples of the former occur chiefly between half tide and 

 low-water mark, the best site being at the verge of the latter, 

 and this more especially as regards Dodecaceria. Leucodore 

 is not only abundant in the substance of the rocks themselves, 

 as mentioned by Mr. Lankester, but swarms under the spread- 

 ing base of Gorallina^ though, on account of the inconspicuous 

 nature of the apertures in the latter, little or no trace of the 

 borings can be observed until the surface is split oiF. Besides, 

 in this (littoral) region there are numerous flattened stones, 

 one or two feet square, that have their surfaces quite worm- 

 eaten by the perforations of the Annelids, whose now vacant 

 galleries have been considerably enlarged by the action of the 

 sand and surf. Occasionally the borings in these large stones 

 were arranged in a linear series, the worm having attacked 

 the commencing fissures as the most vulnerable parts of the 

 mass. At White-Clifl" Bay, again, the perforations in the 

 chalky rocks abounded in the same region, and were of a 

 somewhat larger size than those made by our northern ex- 

 amples. 



Descriptions of the general structure of Leucodore have been 

 published by theAbb^ Dicquemare, Dr. Johnston, MM. ffirsted, 

 Grube, Clapar^de, and Keferstein ; so that my remarks at pre- 

 sent shall be confined to the tentacles, bristles, hooks, and 

 anal segment. 



The tentacles (PI. XIX. figs. 1 & 2) are a pair of very mobile 

 muscular organs, possessing in each case a ciliated furrow on the 

 inner side. Dr. Jolmston being in error in averring that the in- 

 ferior side is so supplied. Dr. Strethill Wright* has given a 

 somewhat minute account of their microscopic appearance in 

 * Edinb. New Phil. Journ. 1857, vol vi. p. 90. 



