THE ANATOMY OF PHARELLA ORIENTALIS, DUNKER 

 AND TAGELUS RUFUS, SPENGLER. 



Bv H. H. BLOOMER. 

 (Plate X.) 



I wish first to acknowledge my indebtedness to the director of the Natural 

 History Department of the British Museum, Professor E. Ray Lankester, 

 F.R.S., and to Mr. Edgar A. Smith, I.S.O., by whose courtesy I have been 

 enabled to examine a specimen of each of the above species. 



Pharella opientalis, Danker. 



^ ■■ External Characters. 



The specimen measures 14.5 cm. long, 4.7 cm. deep, and along the 

 dorsal surface is slightly curved upwards. The mantle lobes from a 

 position over the posterior part of the anterior adductor muscle, take a 

 deep curve and pass some distance posteriorly before their concrescence, 

 thus the pedal aperture though lying anteriorly extends over the anterior 

 adductor muscle, and on the ventral surface still further posteriorly. The 

 muscles of the pallial edge (Fig. 1, P.M.) form a deep band, and the 

 exterior margins of the lobes are crenulated all round them. The perio- 

 stracum passes from the pallial edges to the valves of the shell and is abun- 

 dant at the posterior end. The flaps on the mantle lobes bordering the 

 pedal aperture are very narrow. There is no fourth aperture. The 

 proximal portion of the siphon is strongly developed, while the free 

 portions are extremely short. The tentacles bordering the siphonal 

 openings are very long, particularly the outer ones (Fig. 1, S.T.), some 

 measuring as much as 8 millim. long. The smaller tentacular fringe 

 extends a considerable distance anteriorly along the concresced portion 

 of the mantle lobes, both dorsally and ventraliy. 



The foot (Fig. 1, F.) is long, of a nearly uniform depth and axe- 

 shaped at the distal end. 



The retractor pedis posterior muscle (Fig. 1,P.R.P.) is long, thereby 

 shortening the distance between the posterior adductor and the siphon. 

 At the posterior end the inner parts of the bases of the gills are joined 

 together for about only one -third of the distance between the siphon and 

 the foot. 



The labial palps are relatively short and wide, the outer ones being 

 especially wide. 



