PLATE XIX 



1. Strpmbus pugilis. 



2. Murex saxaidis. 



3. Hatyoiis vulgaris, its shell taken away, seen on the back, and the edges 



of the branchial cavity put asunder. 



A. The large muscle which attaches the animal to the shell. 



a. The anus. ] c. The viscous organ. 



bb. .. branchiae. j d. .. heart in its pericardium . 



4. HalyotiSj etc. the pericardium and branchial cavity opened. 



d. The heart. 



e. .. right auricle. 



f. .. left auricle. 



g. .. heart surrounding the rectum. 

 ii, . . branchial arteries. 



A. The large muscles ;ibove. 



a. .. anus. 



bb. .. branchiae. 



c. .. viscous organ. 



The heart and large vessels magnified. 

 a. i. As the preceding figure. 

 /?. The light branchial vein, 



/ 



