BLOOMER : ANATOMY OF CULTELLUS AND AZOIi. 7 



SoLECURTCS (Azor) ANTiaUATUS (Pult.). 



The one specimen examined from the English Channel is imperfectly 

 preserved, and is much swollen laterally. The measurements, from the 

 shell, are 47 mm. aiitero-posteriorly by 21 mm. dorso-ventrally. There 

 is a .slight lateral constriction towards the centre of the ventral surface. 

 The mantle is muscular and strongly formed. 



The pedal aperture extends from the anterior adductor muscle 

 about halt-way along the ventral surface of the mantle. The inner 

 longitudiiuil fold or vt'lum is short and not so well developed as the 

 middle longitudinal fold which prominently projects ventrally. The 

 union of the two velar processes, terminating the pedal aperture, 

 encloses the posterior portion of the mantle-cavity, and is also 

 continuous with the veiitral wall of the siphon. Similarly, the 

 mantle covering the dorsal surface of the posterior adductor muscle is 

 continuous with the dorsal siphonal wall. 



Ventrally to the posterior adductor muscle (Fig. 2, P. A.) lies the 

 musculus cruciformis, and near it commences tlie fusion of the proximal 

 ])ortion of the siphon with the mantle; still, from that position the 

 mantle-lobes extend some distance posteriorly. 



The siphon is very muscular, with its proximal part (Fig. 2, Ex.S., 

 In.S.) extending a considerable distance rearwardly beyond the fusion 

 of its lateral walls with the mantle. Internally from the junction of 

 the tubes with the proximal portion is on each side a process of the 

 lateral wall (Fig. 2, -S.it.), which runs just above the siphonal retractor 

 muscle to the posterior adductor muscle. To the free edge of tliis 

 process is attached the basal portion of the gills, thus completing the 

 division of the inhalent from the exhalent chamber. The siphonal 

 tubes are likewise large and long. The edge of the mantle carries 

 a minute tentacular fringe; it is, however, a little more distinct near 

 the anterior adductor muscle, wliilst there is no sign of it on the 

 siphon or at the free end of the tubes. 



Musculature. Pallial Muscles. — The muscles of the mantle 

 (Fig. 2, 3r.L.) consist of the radial fibres and the circumpallial or 

 longitudinal ones nearer the edge, but the latter are more numerous 

 in tlie part supporting the velum. The anterior adductor muscle 

 (Fig. 2, A. A.) spreads out somewhat towards each end, where it is 

 moderately deep and wide, but is much longer ventrally than dorsally 

 owing to the convexity of the siiell. The posterior adductor muscle 

 (Fig. 2, P. A.) is large and, like the anterior one, spreads out towards 

 each end, and is also longer ventrally than dorsally. The musculus 

 cruciformis (Fig. 2, 31. C.) is situated on the inner surface of the 

 nmntle ventrally to the posterior adductor muscle, and its two branches 

 on each side gradually diverge, the one going anteriorly and the other 

 ]H)steriorly. lioth are then inserted into the shell. The siphon is 

 characterized by the rearward prolongation of its proximal portion 

 (Fig. 2, lix.S., In.S.), the same being all in one piece. On each side 

 the muscle-fibres of its walls are drawn together into a round and 

 powerful muscle (Kig. 2, S.R.3L), which afterwards penetrates the 

 mantle and, spreading out into a large ovoid-shaped disc, becomes 



