PIRATE XXVIII— Continued. 



Cyrtina CRASSA, Hull. 



Figs. 13, 15. Two views of the exterior of a large individual. 



Coniiferous limestone. Phelps, N. Y. 

 Fig. 14. A cardinal view of a smaller individual, somewhat restored at the apex ; showing the imperforate 

 deltidial covering and the irregular growth of the shell at the cardinal extremities. 

 Corniferous limestone. Canandaigua, N. Y. 



CvRTiNA UM150NATA, Hall, var. Alpenknsis. var. uov. 



Figs. 16, 17. Views of an individual of normal size at this locality, but much larger and more freely jili- 

 cated than the Iowa forms of C. timbimata. 



Fig. 18. The conjoined valves split along the median septum ; showing the extreme anterior extension of 

 the lattei', its acute anterior extremity, and the penetration of its median edge beyond the base 

 of the dental lamella. 



Kig. 19. Lateral view ; showing the form of the spiral cone, its extension into the cavity divided by the me- 

 dian septum, and the projection of the loop downward and toward the brachial valve. X 'H- (c.) 



Fig. 20. Front view of a preparation ; showing the normal shajie of the spiral cones, which are somewhat 

 con.stricted at their bases, expand for about one-half their longlh and thence taper very gradu- 

 ally, terminating in blunt extremities. The form of the crura and loop is also shown. X H. (i^.) ' 

 Hamilton group. Alpena, Michigan. 



Cyktina Ha.miltonensis, Hall, var. recta, Hall. 



Figa. 21, 22. Views of a normal example ; showing the high, erect carilinal area. 

 Hamilton gi-oup. Westei'ii New York. 



Cyktina Hamilton ensis, Hall. 



Fig. 23. Axial section of the combined valves ; showing the form of the median septum and the suppoiled 

 dental plate. 



Fig. 24. An individual sectioned transversely at about the middle of the cardinal area; showing the rela- 

 tions of the deltidial covering, dental plates, median septum and spiral cones. 



Fig. 25. A cardinal view of an internal cast of conjoined valves. 



Fig. 26. The interior of abrachial valve ; showing cardinal process, socket-walls and muscular impi-ession. 



Fig. 27. The exterior of a pedicle-valve with slightly distorted umbo. 



Fig. 28. Opposite side of the same specimen ; showing the elongate foramen on the deltidial plate. 



Fig. 29. An internal cast of the pedicle-valve ; showing the position of the median septum. 



Fig. 30. A pi-eparation, showing the position ol the spiral cones in the pedicle-valve. X 2. (c.) 

 Hamilton group. Localities in Western New York and Ontario. 



Fig. 31. Cardinal view of a sjiecimen in which the spii'als have been partially silicified. X 2. 

 C'ornifei'ous limestone. Falls of the Ohio. 



Fig. 32. An internal cast of the brachial valve ; showing the adductor scars. 



Fig. 33. Knlargemeut of the articulating appaiatus of the brachial valve ; showing cardinal process, den- 

 tal sockets and socket- walls. 



Hamilton group. Western New York. 



Fig. 43. An enlargement of the external surface ; showing the tine pustules. 



Fig. 45. An enlargement of the shell structure ; showing the inuictte of various sizes, penetrating the tibi'ous 

 layers. 



Fig. 46. A portion of a transvei'se section of the umbonal region ; showing the deltidial covering, and the 

 thickened dental lamellae at their union with the median septum, the edge of the latter extend- 

 ing into the deltidial cavity. X 3. 



Fig, 53. The deltidial portion of the pedicle-valve enlarged ; showing the elongate foraminal apei'ture and 

 the tine ci'oss striation of the deltidial covering. X 3. 

 Hamilton group. Widder, Ontario. 



