BRISTOL NATUKALISTS' SOCIETY. 
From the Bristol Daily Post of December U/A, 1865. 
j The usual monthly mepting, which was held at the Pbilo- 
, [BODhical Institution on Thursday evening last, Dec. 7th, 
[was well attended by the members, several visitors alao, 
Iboth Udies and gentlemen, showing their interest in the 
|fio<>iety'8 proceedings by their presence. Mr. W, Sanders, 
F.R S , president, havine: taken tbe chair, ciUed attention to 
jthe largft Bumber of valuable books on the table, which 
jforme(l the nucleus of the society's library, and after point- 
ing out that pome were donations and others obtained by 
purchfise, spoke of the necessity of obtaining farther contri- 
! buttons, both of money and books, in order adequately to 
icarry out the objects of the library. The hon. secretary 
announced that the following names had been added to the 
largely incretsing list of members : —Messrs. Christopher 
.lames and Frederick Seed, M^jor Austen, and the Rev, 
Henry Girdlestone ; a'so that Prof. Backman had been elected 
a corren pond i pgr member of the society. 
Mr. Henrv K. Jordan, F.G.S., read a paper on " The Rock- 
boring Mollusci." The perforation of rock by various 
species of shell- fish had occnpied the attention of naturalists 
from as early a period as 1684, and even at the present time 
observers were not agreed upon the manner in which it was 
effected. In Messrs. Forbes and Hanley'a standard work 
five theories were put forward. That the- perforation was 
caused: — !. By the rotation of th<5 valves of the shell, which 
acted as an auger. 2. Br the rasping of siliceous particles 
imbedded in the soft body of the animal. 3, By currents of 
! water directed on the rock by cilia covering the body of the 
animal. 4. By the secretion of an acid, which acted 
chemically upon the rock. 5. By the combined action 
of rasping and an acid. The author, stating that 
the second and third theories were open to very 
obvious objections, therefore meeting with slight acceptance, 
and that the fifth was simply a combination of the first and 
fourth, proceeded to urge objections to those two. With 
regard to the shell being the instrument of perforation, it 
was exceedingly fragile in many cases, and often less hard 
than the rock itself- nor was it of a shape suitable for 
boring; besides, unleps the foot were pr<»truded, which 
would separate the shell from the rock, the animal would 
have no power to rotate its shell. The chemical theory was 
open to many objections. There was no acid known which 
would dissolve limestone, sandstone, amber, wood, &c., in- 
differently, and if an acid were secreted, no organs for 
which had been found, it would probably dissolve the shell 
as well as the rock. Another theory had been lately pub- 
lished, according to which the hyaline stylite, a special 
organ, rhe use of which was not fully understood, was the 
instrument of perforanon. but it wfcs also found in molluscs 
which did not bore. Careful observation for many years hnd 
induced the author to consider the principl« put forth 120 
years ago bv Sellius, a Dutch naturalist, and now 
sufiporteH bv Mr. .J. Gwyn Jeffries as the true one— viz., 
that the foot of the mollusc, by pressure applied during 
the rev(d<7ing motion, caused the perforation. Mr. 
.lord >n was disposed to consider that the shell rotated as 
well as the foot. When the mollusc recommenced boring, 
the foot was protruded, and the shell was thus lifted, and 
jammed in the upper and smaller part of the hole, the whole 
force of the animal being then expended in pressing the foot 
agiinst the bottom, when a partial revolution was made, the 
shell remaining stationar}'. The adductor muscles were next 
contracted, drawing the valvts together, and thus a partial 
ietracti(*n of the foot taking place alao, the shell was 
liberated, which then rotated to its normal position, and in 
doing this, certain traf.sverse strijB were formed, which it 
was Difficult to account for in anv other wav. The detritus 
