BRYOZOA. 



643 



forms. When the various species now referred to the genus are 

 better understood, these two sections will probably be separated 

 generically. A suggestive resemblance to Cyclostomatous Bryo- 

 zoa is represented by H. imbricatu and H. spiniformis. The in- 

 ternal structure of two typical species is represented in the ac- 

 companying cut. 



Fig. 18, a, b, c, d, e. Sections of Helopora frag ilis, x!8, Clinton group, Hamilton, On- 

 tario. Fig. a, tangential section as it appears in the ferruginous matrix; in these ex- 

 amples the extreme outer region is destroyed; b, tangential section of another exam- 

 ple, showing acanthopores at surface, etc. ; c, transverse section near upper extremity 

 of segments; d, same at base; e, vertical section. 



Fig. /, a, h, sections of Helopora Kndstromi, n. sp. x!8. Upper Silurian. Gotland; 

 /, tangential section showing form of zooacia and acanthopores; g, transverse section; 

 h, vertical section. The cylindrical or slightly club-shaped segments of this fine species 

 vary in length from 10 to 15 mm., in diameter from 1.3 to 1.8 mm. Upper extremity 

 flattened, slightly concave centrally; lower end moderately convex. Zooecia arranged 

 in quincunx: measuring lengthwise seventeen in 5 mm.; diagonally four in 1 mm. 

 Apertures direct, oval, with a narrow peristome set into a rhomboidal or hexagonal 

 concave space. Between the ends of the cells a strong acanthopore. It gives me great 

 pleasure to propose the above name in honor of the talented Swedish Palaeontologist, 

 Dr. Gustav Lindstrom, to whose kindness I owe the opportunity of studying this beauti- 

 ful species. 



