1903.] NATURAL SCIENCES OF PHILADELPHIA. 369 



(12) Sphincter trunci qiiartus, Sph.tr. IV, interrupted dorsally but 

 generally closed ventrally (Gast's rm 9). 



(13) Sphincter trunci quintus, Sph.tr., V, dividing into three 

 branches, interrupted dorsally and ventrall}' (Gast's rm 10). 



(14) Sphincter trunci sextus, Sph.tr. YI, paired, latero-ventral on 

 each side of the foot (Gast's mb 3). 



(6) Longitudino-circular muscles. 



(15) One pair, L.-C.M., passing from the posterior end of the body to 

 about the middle of the trunk, then each turns ventrad (Gast's dim 3). 



(c) Longitudinal muscles. 



(16) Retractor coronse primus, i^.c. 7, on the antero-dorsal surface of 

 the corona (Gast's dim 1). 



(17) Retractor corona secundus, R.c. II, on the postero-dorsal sur- 

 face of the corona (Gast's dim 2). 



(18) Retractor coronse tertius, R.c. Ill, the innermost ventral pair, 

 attached at the foot, passing forward and outward to insert upon 

 Sph.C. I (Gast's vim 1, but with a different anterior relation). 



(19) Retractor coronse quartus, R.c. IV, paired, ventral (Gast's 

 vim 2). 



(20) Retractor coronte quintus, R.c. V, inserted posteriorly at the 

 sides of the foot, passing anteriorly to insert on Sph.C. I (it is much 

 longer than Gast's vim 3). 



(21) Retractor coronse sextus, R.c. VI, paired, each with two 

 branches ending posteriorly on the sides of the trunk, a single anterior 

 branch inserting on Sph.C. I, and with two small lateral branches 

 (which for the sake of clearness are not shown on the lateral view of the 

 animal). (This corresponds more or less to Gast's vim 4.) 



(22) Compressor trunci, C.T., paired, subject to considerable varia- 

 tion in form, a very thin but broad muscle always with several branches, 

 extending back to the sides of the foot and anteriorly inserting upon 

 R.c. Ill, R.c. IV, R.c. V. 



II. Visceral muscles (those which are entirely separated from the 

 hypodermis, or in which only one end is attached to the hypodermis, 

 which is the more usual condition). 



(a) Circular muscles. 



(23) Retractor mastacis, r.m., paired, a short muscle connecting the 

 side of the mastax with L.-C.M. 



(24) Sphincter oesophagi, sph.oes. (found by Gast). 



(25) Sphincter ani, sph.an. (found by Gast). 



(b) Dorso-ventral muscles. 



(26, 27) Depressor trunci prinuis et secundus, d.tr. 1 and 2, two pairs, 

 24 



