118 bloomer: anatomy op pharella and tagelus. 



portion of the sipiion, innervating it and the dorsal integument, and 

 apparently joining the outer circumpallial nerve. 



Tagelus rufus, Spengler. 



External Characters. ' 



The specimen measures 5.7 cm. long and 2 cm. deep. The mantle 

 lobes (Fig. 4, M.L.), w'hich take a slight curve forwardly from the anterior 

 margin of the anterior adductor muscle, are not concresced along their 

 ventral surface, but are joined together below the extreme siphon al end 

 by a round transverse muscle (Fig. 4, M.C.), the ends adhering to the 

 valves of the shell, and thus resembling the adductor muscles, conse- 

 quently the pedal aperture extends from the anterior adductor muscle to 

 the siphon. There is no fourth aperture. At the posterior end the mantle 

 lobes proceed some distance beyond the proximal portion of the siphon, 

 giving off close to their posterior edges lateral processes (Fig. 4, P.L.P.) 

 which encircle and are connected, with the siphon, thus completely en- 

 closing the posterior end of the pallial chamber. 



The teeth of the shell are not very prominent, and do not penetrate 

 into the viscera as in S. strigillatus. The proximal portion of the siphon 

 is short,']while the free portions (Fig. 4, In. /'. and Ex. S' .) are of consider- 

 able length, the exhalent being longer than the inhalent one, but the 

 openings by which they communicate with the pallial chamber are small. 

 Large siphonal retractor muscles (Fig. 4, S.R.3I.) are present and from a 

 large surface adhere to the valves of the shell. The edges of the mantle 

 lobes and the siphon are not characterised by carrying a tentacular fringe. 

 The foot (Fig. 4, F.) is large, comparatively short, and very deep. The 

 inner parts of the bases of the gills are joined together. 



Musculature. 



i. Pallial Muscles. — The muscles of the pallial edge commence at 

 the anterior adductor muscle as a deep band. This band, after taking 

 a slight curve, anteriorly, passes posteriorly and gradually decreases in 

 depth until it reaches the proximal siphonal end, where the two mantle 

 lobes are joined together by a round transverse muscle, the musculus 

 cruciforrais (Fig. 4, ilf.C.) described by von Ihering ''^^ and stated by him 

 as being an important character of the super-family Tdlinacea, con- 

 firming the views of Dall. He believes this cruciform muscle is a special 

 development of the fibres of the mantle edge, and functionally may serve 

 as a secondary adductor. 



The siphonal retractor muscles (Fig. 4., S.R.M.) run a short distance 

 anteriorly along the mantle lobes, they pass through them, and spreading 



2. Proc. Acad. Nat. Sci. Philad., 1900, pp. 480, 481, 2 figs. 



