PLATE IV H. 



Leg'end. pa. Posterior adductor scars. m. Median muscular fulcrum. 



aa. Anterior adductor seal's. v. Vascular sinuses. 



b. Brachial muscular scars. 



CRANIA, Eetzius. 



Page 14.T. 



Crania L.islia, H;ill. 



Fig. 1. Four individuals attached to the pedicle-valve of 8treptorhynclms ]}lanuiiibonum. 

 Hudson River group. Oxford, Ohio. 



Crania agaricina, sp. nov. 



Fig. 2. An individual attached to a branch of Teematopora ; showing the characteristic sparse and 

 relatively coarse :-adiating I'ibs. X 3. 



Lower Helderberg gi-onp. Near ClarksoiJle. iV. Y. 



Crania pulciiella, sp. nov. 



Fig. 3. An individual attached to the valve of Orthis suhearinata. It ditfei's from the preceding species 

 in its finer, more numei'Ous ribs and greater size. X 2. 



Lower Helderberg group. Near ClarJcsville, N. Y. 



Crania Bordeni, Hall and Whittield. 



Fig. 4. An individual attached to a valve of Sjm-ifer Oweni; showing the very fine radiating striae, and 



the conformation of the upper vah'e to the surface of attachment. 

 Fig. 5. Profile of the same specimen. 



Hamilton limestone. Clarke county, Indiana 



Crania crenistriata, Hall. 



Fig. 6. The inteiior of an upper valve ; showing the sti-ong antei-ior adductor scars and very faint poste- 

 rior adductors. X 2. 



Hamilton limestone. Falls of the Ohio. 

 Fig. 7. A portion of a cast of the internal surface in a decomposed chert ; showing the tilling of vei-tical 

 canals. X 25. 



Corniferous limestone. Canandaig iia, N. Y. 

 Fig. 8. The interior of an uppei' valve ; showing the vei-y sti-ong anterior adductor scars with mai-- 

 gins elevated, and the moi'e obscure posterior scars. X 3. 



Hamilton limestone. Falls of the Ohio. 

 Pig. 9. The exterior of a large uppei- valve. Natural size. 



Hamilton group. Canandaigua Lake, N. Y. 

 Fig. 10. A smaller uncompres.sed individual. 

 Fig. 11. Profile of the same. 



Hamilton group. Western Nexo York. 

 Fig. 12. A valve of the same, or a closely allied species, attached to Orthis im.pre.fsa. X S. 



Upper Devonian. Rockford, Iowa. 



Crania Rowleyi, Gurlcy. 

 Pig. 13. An individual showing the upper valve. X 2. ^ 



Choteau limestone. Pike county, Missouri. 



Crania setigera, Hall. 



Fig. 14. An individual, referi-ed to this species with some hesitation ; attached to a bi'anch of Monticoli- 

 PORA. It will be observed that for some distance about the antei'ior edges of the shell, where 

 the valves opened foi' the. admis.sion of food-bearing watei'-curi'ents, the outward growth of 

 the bi-yozoan cells has been obstructerl. X 2. 



Trenton horizon Minneapolvi, Minne.iota. 

 Fig. 15. An upper valve. X 2. 

 Fig. 16. Profile of the same. X 2. 



Trenton limestone. Mineral Point, Wisconsin. 



Crania .^pinigera, Hall. 



Fig. 17. The original specimen ; an individual attached to the shell of Rhynchoniila Strickland!. The 

 ornamentation consists of radiating I'ows of shar]ily defined tubei'cles. X 3. 

 Niagara grouji WoMron, Indiana. 



