286 MISSISSIPPIAN BRACHIOPODA 



specimen which has come under observation is apparently an adult indi- 

 vidual, judging from the thickening of the valves at their free margins, 

 and is many times smaller than adult examples of the Devonian A. spinosa. 

 Size alone would perhaps not be a character upon which a species could 

 be established, but in addition to this the brachial valve is considerably 

 less convex than the pedicle, while in A. spinosa the brachial valve is 

 the more convex. 



Horizon. Glen Park limestone of the Kinderhook. 



Family SPIRIFERID^E 

 Genus CYRTINA Davidson 



Description. Shells small, semipyramlidal in form, with usually non-pli- 

 cated mesial fold and sinus, and simply plicated lateral slopes. Pedicle 

 valve with a high, vertical or arched cardinal area which may be sym- 

 metrical or more or less distorted, the delthyrium narrowly triangular, 

 closed with a convex pseudodeltidium which is perforated at a point be- 

 low the apex by a subcircular, direct or oblique foramen, or may be with- 

 out any opening. Internally the dental lamellae are strongly developed 

 and converge rapidly towards the inner surface of the valve, before meet- 

 ing which they become joined in a single median septum which con- 

 tinues to the floor and extends anteriorly beyond the center, of the 

 valve. Brachial valve very shallow, with narrow, inconspicuous cardinal 

 area. Internally the cardinal area consists of a double apophysis from 

 the sides of which diverge the strong crural plates; the spiral cones are 

 directed obliquely towards the middle of each lateral slope of the pedicle 

 valve, the jugum is continuous, its branches being directed upward and 

 forward, uniting at their extremities. Shell substance strongly punctate. 



Remarks. The genus Cyrtina has its greatest development in the Devo- 

 nian faunas, being represented in only the earlier portion of Mississippian 

 time. It differs from Spiriferina, another strongly punctate shell, 

 in the union of the dental lamellae to form a spondylium supported by a 

 median septum, as well as in the more conspicuous semipyramidal form 

 of the shell. 



CYRTINA ACUTIROSTRIS (Shumard) 

 Plate XXXV, Figs. 6-21 



1855. Cyrtia acutirostris Shumard, Geol. Rep. Mo., p. 204. pi. C, figs. 



3a-c. 

 1894. Cyrtina acutirostris Hall and Clarke, Int. to Study of iBrach., pt. 2, 



pi. 29, fig. 18. 



1894. Cyrtina acutirostris Keyes, Mo. Geol. Surv., vol. 5, p. 89, pi. 39, 



figs. lOa-b. 



1895. Cyrtina acutirostris Hall and Clarke, Pal. N. Y., vol. 8, pt, 2, pi. 28, 



figs. 38-42, 44, 54. 



