PLATE IV II, 



Leg-end. pa. Posterior acliUictoi- scars. m. Median muscular fuli-ruiii. 



aa. Anterior adductor scars. v. \'a.scular sinuse.s. 



b. Biailiinl nuisculai' scars. 



CllANlA, Retzius. 



Page US. 



Crani.\ L.elia, II;ill. 



Fig. 1. Four individuals attaclieil to the pedicle-valve of Strrpt orb yii elms planambunwm. 

 Hudson River grouji. Oxford, Ohio. 



CkA.NIA AGARICINA, .sp. IIOV. 



Fig. 2. An indiviilual attached to a branch of TRKMATOPOR.i ; showing the charactm'istic .sparse and 

 relatively coarse radiating ribs. X 3. 



Lower Helderberg group. Near Clarksvllle. N. Y. 



(.^RANIA rULCllELLA, sp. UOV. 



Fig. H. An individual attached to the valve of Orthis suhcarhiata. It differs from the preceding species 

 in its tiner, more numerous ribs and greater size. X 2. 



Lower Heliierberg group. Near Clarksvllle, N. Y. 



Crania Borueni, Hall and Wliitliuld. 



Fig. 4. An individual attached to a valve of Spirifer Oiveni; showing the very tine railiating stria?, ami 



the confoi'tnation of the upper valve to the surface of attacliment. 

 Fig. 5. Pi'otile of the same specimen. 



Hamilton limestone. Clarke cmmty, Indiana 



Crania crenistriata, Hall. 



Fig. 6. The interior of an n])pei' valve ; showing the strong anterior 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 decomjiosed chert ; showing the tilling of vei-tical 

 canals. X 25. 



Corniferous limestone. Canandaig iia, N. Y. 

 Fig. 8. The interior of an upper valve ; showing the very strong anter'ior adductor scars with mar- 

 gins elevated, and the more obscure posterior scar.s. X 3. 

 Hamilton limestone. Falls if the Ohio. 

 Fig. 9. The exterior of a large upper valve. Natural size. 



Hamilton group. Canaiida,'iy>ia Lake. N. Y. 

 Fig. 10. A smaller uncompressed indiviilual. 

 Fig. 11. I'rotile of the same. 



Hamilton group. JVestern New Yo7'k. 

 Fig. 12. A valve of the same, or a closely allied species, attached to Orthis iiiipre.wa. X T). 

 Upper Devonian. Mockford, Iowa. 



Crania Rowley i, (iiirle\-. 



Fig. 13. An inilividnal showing tlie upper valve. X 2. 



Choteau limestone. Pike county, Missouri. 



Crania setigera, Hull. 



Fig. 14. An individual, referred to this species with some hesitation ; attached to a branch of Monticcli- 

 PORA. It will be observed that for some distance about the anterior eilges of the shell, where 

 the valves opened for the admission of food-bearing water-currents, the outward growth of 

 the bryozoan cells has lieen obstructeil. X 2. 



Trenton horizon illimeapoUs, Minnesota. 

 Fig. 15. An upper valve. X 2. 

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



Trenton limestone. Mineral Point, T\^isco7isin. 



Crania .spinioera, Hall. 



Fig. 17. The original specimen ; an individual .attached to the shell of Hhynchimiila Stri<klandi. The 

 ornamentation consists of riidiating rows of sharjily ilefined tubercles. X S. 

 Niagarii grou]i JVntilrnn. Indiaiui. 



