ii4 NORTH AMERICAN INDEX FOSSILS. 



15. Apertures in 3 to 7 rows ; reverse side not striated. 



LVI. Reteporidra. 

 10* Regularly anastomosing, or connected by scarcely recognizable dis- 

 sepiments 16. 



16. Apertures in two rows, carinae expanded sometimes to width of 



branch LI V. Loculipora . 



16. Apertures in 3 to 7 rows, no median carina. LVI. Reteporidra. 

 D. Zoarium a repeatedly branching frond, the branches rarely united by dissep- 

 iments (sometimes wanting) XXX' 



XXX Branches flexuous and irregular 11*. 



II* Apertures angular \ XLIX. Drymotrypa. 



II* Apertures rounded LIX. Thamniscus. 



XXX Branches rigid, parallel and regular, sometimes absent 12*. 



12* Branches short, free, apertures in two rows with median keel. 



LXIL Pinnatopora. 

 12* Branches long, oblique, smaller than stipe, occasionally united by 



thin dissepiments LXIII. Ptilopora. 



12* Branches wanting LXIV. Diploporai'ia. 



D. Zoarium of more or less cylindrical branches, preserved generally as fragments. 



xxxx- 



XXXX Branches in articulating segments or articulated basally 13*. 



13* Segments with one of several faces longitudinally striated and with- 

 out apertures LX V. A rlhrostylus. 



13* Segments celluliferous on all sides 17. 



17. Segments uniting by terminal articulation, ends often swollen. 



LXVI. Helopora. 



17. Segments with terminal and lateral (pinnate) articulation, the 



segments commonly showing the articulating facet on the side. 



LXVII. Arthroclema. 



17. Slender, articulating only at the pointed base, branching above. 



LXVIII. Nematopora. 



XXXX Branches not articulating 14*. 



14* Branch with one side striated and non-celluliferous, the other with 



two rows of pores LXIV. Diploporaria. 



14* Branches celluliferous on all sides 18. 



18. Branches solid p. 



p. Apertures in diagonally intersecting series gg. 



q-g Without peristomes 33. 



33. Frequently branching LXIX. Rhombopora. 



33. Simple or rarely branching, pointed at base. 



LXXI. Bactropora. 



%g. With peristomes 44. 



44. Compressed, dichotomously dividing. 



XCVI. SticMrypa 



t>. Apertures in longitudinal series hh 



hh. Cylindrical with pits between apertures. 



LXXII. Streblotrypa. 



hh. Cylindrical without pits Orthopora. 



18. Branches hollow q. 



q. Apertures with depressed vestibules, interspace narrow. 



LXX. Coeloconus. 



