ON THE ANATOMY OF SPECIES OF CULTELLUS AND AZOR. 



By H. H. Bloomer, F.L.S. 



Read 10th November, 1911. 



PLATE I. 



I DESiKE to express my thuiiks to Mr. Edgar A. Smitli, I.S.O., 

 of the British Museum, for kindly permitting me to examine the 

 following : — 



CuLTELLUS CULTELLUS (Linn.). 



The specimen examined from the Indian Ocean measures 61 mm. 

 antero-posteriorly by 17 mm. dorso-ventrally. Along the dorsal edge 

 it is straight, except at the anterior end, where it bends upwards. 

 The other edges are curved. 



The mantle-lobes are united in front of the anterior adductor muscle 

 and pi'ojeet anteriorly. The pedal aperture occupies nearly the 

 anterior half of the ventral surface, tlien the pallial edges coalesce. 

 Posteriorly the other openings are only the siphonal ones, there being no 

 fourth aperture. The lobes bordering the pedal aperture carry a minute 

 tentacular fringe on the middle longitudinal fold, the same being 

 a little more evident at the anterior end. The inner longitudiiuil fold 

 or velum on the ventral surface of the animal is shallow, but becomes 

 deeper anteriorly. The whole of the external surface of the mantle is 

 mottled with snuill brown markings, which to an extent correspond 

 to, and account for, the mottled appeai'auce of the periostracum 

 covering the shell, the more distinctive feature of this species. 



The siphon is nearly all in one piece, the free portions being 

 very short. The siphonal chambers are shoit, but deep, and tlieir 

 apertures are bordered by a long tentacular fringe, the outer tentacles 

 being- jnuch longer tluin the inner ones. The fringe continues dorsally 

 and ventrally, though in a considerably lesser degree, and gradually 

 disappears. Fig. 1 (Jix.S., In.S.) shows the free portions of the 

 siphon to point dorso-posteriorh', but this is probably due to the 

 greater contraction of the muscles controlling the exhalent j)art. 



The foot (Fig. 1, F.) is apparently large and muscular, with the 

 distal part pointing anteriorly. Its exact length, however, cannot be 

 determined, as a portion of it is missing. 



Musculature. Pallial Muscles. — The anterior adductor muscle 

 (Fig. 1, A. A.) is a broad muscle, with the anterior part turning 

 sharply upwards, and increasing in depth as it pi'oceeds posteriorly. 

 It is joined at the anterior end with the mantle-lobes, and at the 

 posterior one with the protractor pedis anterior muscles. Compared 

 with the same muscle in Soleu pellucidus it is neither so broad nor so 

 deep, and at the posterior end the bend ventrally is not so pronounced. 



The posterior adductor muscle (Fig. 1, P. A.) is large, being both 

 wide and deep, and is much larger than that of S. pellucidus. It is 

 flattened dorsally and curved ventrally. Anteriorly it is connected 

 with the retractor pedis posterior muscle, and posteriorly with the 

 mantle-lobes. 



