60 - ZOOLOGY. 
is soon after able to commence perforating. The transparent shell of the 
embryo soon disappears, and is replaced by the permanent one. In boring, 
the wood is generally entered across the grain, but afterwards the animals 
turn in the direction of the fibres, though they are subject to be continually 
turned from their course by each other, the wood being perfectly honey- 
combed by their number, and often in the course of a year. 
Fam. 8. Tubicola. The name indicates the tubular form of the external 
protection in this family. The tube is secreted by the mantle, and its 
continuation covering the siphons. In Aspergellum (pl. 75, jig. 71) both 
valves form part of the tube; in Clavagella the valves are placed within a 
short tube, one of them being attached; and in Gastrochena the shell is 
not attached, but inclosed in a tube. The mantle is open in front for the ~ 
passage of a little foot, the siphon and branchiz are usually jong, and the 
palpi are small. These shell-fish inhabit clay, sand, or cavities in stone or 
wood, pierced by themselves. 
The genus Aspergillum was first correctly figured in 1685, by Lister, one 
of the fathers of conchology; but it was many years before its true 
approximate place was known, since it required much sagacity to detect a 
bivalve shell under the form of a tube. We accordingly find it placed at 
one time among univalve genera, and at another with the Annelida which 
form tubes, and Linneeus placed it with Dentalium. The happy idea of 
Aspergillum being a true bivalve is due to De Roissy, and is a remarkable 
example of the detection of natural affinities. A parallel example appears 
in the Planorbis cornuarietis which, to all appearance, was referred to its 
proper genus, but which Sowerby referred to Ampullaria, with none of 
which did it seem to be allied ; but the subsequent discovery of the animal 
proved his reasoning to be correct, although strongly opposed at the time. 
The structure of Clavagella is quite anomalous, the valve of the right side 
forming part of the inside of the tube, and the left valve being free. The 
anatomy is essentially that of a bivalve mollusc, and shows an affinity with 
Aspergillum. It is provided with a small foot. 
The genus (astrochena, Spengler, 1783 (or /istulana, Lam., 1801), is a 
boring shell, sometimes found in calcareous rocks, and sometimes in sand, 
secreting, besides its proper shell, a separate exterior tube; and, as the shell 
may be accidentally found without the tube, after the death of the animal, 
an error was committed in describing the shell alone as one genus, and the 
tube and shell together as another, namely, Fistulana; an error which 
Deshayes was the first to correct, and he accordingly suppresses the latter 
name. Shell symmetrical, and widely gaping anteriorly, without cardinal 
teeth, a ligament posteriorly, pallial impression deeply sinuated, foot small, 
and secreting a byssus. The following species are found in the tertiary 
strata of the United States. Gastrochana ligula, H. CO. Lea, Am. Phil. 
Trans., vol. ix. G. larva, Conrad (Fistulana), Am. J. Scv., 1846, p. 218. 
G. elongata, Desh., Conrad, Vat. Inst. Washington. 
Tribe Hlatobranchia. 
This tribe includes the great mass of OConchifera, after separating the 
preceding one. With very few exceptions, the Inclusa have two adductor 
264 
