PLATE 13. 



Sidonops angulata Lendenfeld. 



Figs. 1-8. — var. megana Lendenfeld (lobose form). 



Figs. 9-12, 22-25. — var. megana Lendenfeld (massive form). 

 Figs. 13-17, 21. — var. microana Lendenfeld. 

 Figs. 18-20. — var. orthotriaena Lendenfeld. 



1, 2. — Stout, choanosomal amphioxes of tlie lobose specimen of var. megana; magnified 40; phot. 

 Zeiss, planar 20. 



3. — A plagiotriaene of the lobose specimen of var. megana; magnified 40; phot. Zeiss, planar 20. 



4. — Apical view of the cladome of an irregular plagiotriaene of the lobose specimen of var. megana; 



magnified 40; phot. Zeiss, achr. aa, compens. oc. 6. 

 5-16. — Cladomes of plagiotriaenes seen from the side; magnified 40; phot. Zeiss, achr. aa, compens. 

 oc. 6: 



5-8, from the lobose specimen of var. megana; 

 9-12, from the massive specimen of megana; 

 13-16, from var. microana; 



5, with long, somewhat unequal, terminally strongly recurved clades; 



6, 8, with long, somewhat unequal, terminally slightly recurved clades; 



7, 13, 16, with unequal, slightly recurved clades; 



9, with short, equal, nearly straight clades; 



10, with short, irregularly curved, somewhat unequal clades; 



11, 15, with medium-sized, equal, slightly recurved clades; 



12, with unequal, nearly straight clades; 



14, with medium-sized, slightly unequal, rather strongly recurved clades. 



17. — Group of spicules from a spicule-preparation of var. microana; magnified 40; phot. Zeiss, planar 



20: 



a, an angularly bent amphiox; b, a nearly straight amphiox; c, the cladomal half of an 

 anatriaene. 



18. — Cladome of an orthotriaene of var. orlliotriaena; magnified 40; phot. Zeiss, achr. aa, compens. 



oc. 6. 



19. — An orthotriaene with angularly bent rhabdome of var. orthotriaena; magnified 40; phot. Zeiss, 



achr. aa. compens. oc. 6. 



20. — Two rhabds of var. orthotriaena; magnified 40; phot. Zeiss, planar 20: 



a, a club-shaped style; b, an amphiox. 



21. — Part of a radial section of var. microana; magnified 10; phot. Zeiss, planar 50: 



a, cortex (sterraster-armour) ; b, spicule-fur. 

 22-24. — Surface views (parts of superficial paratangential sections) of the massive specimen of var. 

 megana; magnified 100; phot. Zeiss, apochr. 16, compens. oc. 6: 



22, an efTerent uniporal opening; 



23, 24, afferent cribriporal openings (pore-sieves). 



25. — Part of a radial section through the superficial part of the massive specimen of var. megana; mag- 

 nified 40; phot. Zeiss, achr. aa, compens. oc. 6: 



a, sterraster-armour; b, a chone; c, a subcortical cavity. 



