AMPLEXOID CORALS FROM ILLINOIS AND ARKANSAS 629 



of counter quadrants somewhat dilated, 

 three grouped in palmate bunches on either 

 side of long counter septum; minor septa 

 rudimentary. 



At slightly earlier stage (fig. 5) in a para- 

 type, septa of counter quadrants much di- 

 lated; septa of cardinal quadrants thin, 

 sinuous. 



Longitudinal section. — Not prepared. 



Occurrence. — All specimens are from thin 

 limestone lenses in Paint Creek shale about 

 10 to 15 feet below the Cypress sandstone, 

 on the south bluffs at Indian Point over- 

 looking the valley of Cache River, in sec. 32, 

 T. 13 S., R. 3 E., Johnson County, Illinois. 



Material. — -Specimens studied, 3; holo- 

 type, no. 47247; figured paratypes, not 

 numbered; all in Walker Museum, Uni- 

 versity of Chicago, collected by Stuart 

 Weller. 



Ontogeny. — 'Early stages not preserved. 



Comparison. — This species differs from 

 the other Chester amplexoid corals in having 

 the septa of the counter quadrants dilated 

 in early maturity, and in having relatively 

 strong development of minor septa. 



The species can be identified externally 

 by its curved conical shape, sparse spines, 

 and common occurrence of the cardinal posi- 

 tion on the convex side of the corallite. 



Remarks. — A. dilatatus has typical so- 

 called "zaphrentid" type of septal pattern. 

 It appears to be related to A. rockfordensis 

 from the Rockford beds (Kinderhook) of 

 Indiana. 



Amplexus expansus Easton, n. sp. 

 Plate 85, figure 8; plate 86, figures 1-3 



Externals. — Ceratoid, slightly curved with 

 apical angle about 30°; epitheca generally 

 with fine encircling striae distally but with 

 septal grooves and interseptal ridges proxi- 

 mally, wrinkled throughout; apical end re- 

 curved, commonly much less flared than 

 rest of coral, with very fine encircling striae, 

 flattened on one side (cardinal side wherever 

 observed) where apparently attached to 

 foreign body; sections reveal rather deep 

 calyx (about § length of corallite) vertically 

 walled and lined with septa. Specimens 

 range in length from about 1.5 cm. to 3.5 

 cm.; diameter of calyx about 12 mm.; early 

 attached portion from 2 to 4 mm. long. 



Transverse sections. — Septa become am- 

 plexoid rapidly, beginning their retreat at 

 stage of about 17 septa. (See "ontogeny" 

 for details.) 



Longitudinal section. — Tubulae nearly all 

 complete, about 8 in 1 cm., recurved proxi- 

 mally near peripheries and with proximal 

 sag in axial region. 



Occurrence. — Fayetteville shale, 6 miles 

 east and 1.5 miles north of Vinita, Okla- 

 homa. Collected by Maurice Wallace and 

 Arthur Bowsher. 



Material. — Specimens studied, 37; holo- 

 type, figured paratypes, unfigured para- 

 types, and topotypes, not numbered; all in 

 the collections of the University of Kansas. 



Ontogeny. — Most of the septa are inserted 



Explanation of Plate 85 



Figs. 7 — Amplexus geniculatus Worthen. Side view; holotype; XI; Illinois State Geological Survey 

 (Worthen collection) No. 2566a. (p. 630) 



8 — Amplexus expansus Easton, n. sp. Side view; para type; XI; University of Kansas, (p. 629) 

 9 — Amplexus adnatus Easton, n. sp. Side view; holotype; XI; Walker Museum No. 47248. 



(p. 627) 

 10 — Amplexus dilatatus Easton, n. sp. Side view; holotype; XI; Walker Museum No. 47247. 



(p. 628) 



