PL ATK IV 



anal leading to arm. si, subtentacular canal. 



g. food groove. r, first radial. 



p,,, pinnule, z, syzygy. 

 pn', first pinnule. 



1. Arm uf left anterior radial of a broken specimen, \. 



2. Slightly oblique view of vault, showing the relation of the interradial plates of the vault and the 



s covering the subtentacular canal and the food groove. ■}. 



3. Interior view of upper pint uf perisomatic vault, showing food groove, the subtentacular canal, and 



the extension of the cceliac cavity aa a groove into cavity of the arm. ;'. 



4. Tli bove, seen edgewise. 



5. Interior view of upper part of interradial space, showing its connection with the edge of the arm 



joints and of the pinnules, i. 



6. Interior view of lower interradial plates, j. 



7. Base of the first pinnule, showing the connection of the lower interradial plates to the pinnule joints 



and to the smaller perisomatic plates, seen in profile. 



8. Showing spongy character of the upper perforated perisomatic plates, magnified. 



9. Exterior upper face of an imperforate interradial plate in the second row. 



10. Lower interior face of the same. 



11. One of the plates of the first row of interradials, exterior face. 



12. Another plate from the first row of interradials, exterior face. 



13. Plate of Fig. 11 seen edgewise to show its thickness. 



14. One of the smaller imperforate interradial plates near the edge of fourth radial. 

 10, 16. Magnified views of reticulation of the interradial plates. 



