MR. R. OWEN ON THE ANATOMY OF CLAVAGELLA. 273 
The ovary! is of a grey colour, forming a mass at the dorsal aspect of the body above 
the great adductor muscle, and extending ventrad on either side the esophagus and 
stomach to the opposite end of the base of the foot. 
All this mass of intestinal folds, hepatic follicles, and ova was covered by a thin 
membrane. The little muscular process, or foot, which passes through the anterior 
slit of the mantle is but 4 lines long, and half a line in breadth: its possible use may 
be to apply a solvent to the rock in which the chamber is excavated. 
The organization of Clavagella, like that of Aspergillum described in the ‘ Reise von 
Afrik’ of Dr. Riippell, is thus seen to be modelled on the type of the Acephalous Bi- 
valves, and follows most closely, in the variations from that type, the modifications 
which have been observed in Gastrochena. 
The lengthened worm-like figure of Aspergillum is exchanged in Clavagella for a 
shorter form, with greater lateral development: and instead of the small rudimentary 
valves, which are enchased, as it were, in the calcareous sheath of Aspergillum, we find 
them here largely developed, and one of them always remaining at liberty, to be ap- 
plied by a powerful muscular apparatus to those offices which are essential to the 
forcible expulsion of the fluid in the branchial cavity, and probably to assist in the ex- 
cavation of its secure abode. 
PLATE XXX. 
Fig. 8. A portion of the rock (calcareous grit), containing the attached valve and 
part of the tube of Clavagella lata. The chamber has been so laid open 
as to show its greatest dimensions, both in length and breadth. 
9. Outside view of the right or free valve of the same specimen. 
10. Inside view of the same, showing the corresponding muscular impressions 
to those of the left or fixed valve. 
11. Soft parts of Clavagella lata viewed from the right side, the dermal layer of 
the mantle, e, being removed. 
12. Soft parts of Clavagella lata, seen from the left side, or that which is in con- 
tact with the fixed valve. (The extremities of the left labial appendages 
only are here seen, no part of the gill being protruded. A bristle is placed 
in the rictus, or opening of the mantle.) 
13. Anterior view of the soft parts of Clavagella lata, after the removal of the 
outer or dermal layer of the mantle. 
14. The same, with the anterior muscular mass reflected to show its internal 
surface ; the visceral mass, composed of the liver w, intestine s, and 
ovary 2, from which the foot y is continued. 
15. Posterior extremity of the siphon. 
16. The principal viscera displayed. 
1 gv. Figg. 12, 14. 2 y, Fig, 14. 
