GASTRIOCEHAS. 87 



Gastrioceras entogonum GabV). 



Plate X, figs. 17-19. 



1861. Goniatiten ento(jonu«^ \\ . M. (iabb. Proc. Acad. Nat. Sci. Phila., ISOl, p. 372. 

 1S!>3. GdKtrioceras entogonum, A. Hyatt, Fourth Ann. Kept. Geol. Siirv. Texas, 

 p. 472. PI. XLVIT, tigs. 49-51. 



The following- description is quoted from Hyatt's paper: 



This species is similar to others of the genus in its ojjen uniliiliei and the areuate 

 trapezoidal outline of tlie whorl in section. The cast is inai-ked l)y d(!ep constrictions, 

 confined to the abdomen, and somewhat less than one-thii'd of a volution apart, or 

 aliout three and tive-tenths to one volution. Those bend forward on either side and 

 then back, forming two crests and a median sinus on the abdomen. The sides are 

 divergent, narrow, and smooth. The abdomen is strongly furrowed and ridged on 

 the shell, and these markings are repeated on the cast. The longitudinal ridges are 

 crossed by strong lines and narrow lamina> of growth, which are to a greater or less 

 extent impressed upon the surface of the cast, as shown in tig. 51 [in Hj-att's 

 paper]. The lines of growth and the constrictions are exactly parallel on the abdomen, 

 and the apertures were prol)ably similar in outline. 



The shell was seen only in small fragments, but there is sufficient of these to 

 show that it was not very thick, and ornamented by continuous ridges mnch 

 sharper than those on the cast. These were crossed and slightly serrated by tine 

 transverse lines, occurring as the edges of narrow laminaj of growth. The sides are 

 smooth except for the presence of the edges of these same laminre. But there is one 

 patch near the line of involution having a ridge with the usual crenulations. The 

 ridges on the venter cross the constriction of the cast below without anj^ intlection, 

 the constriction being caused entirely by the internal thickening of inner layer of 

 the shell. 



This species differs from Gmt. Iviterl of Europe in the smoothness of the 

 shell on the sides and the extent of the involution, which is here coextensive with 

 the abdomen of the whorls, and also in the strong ridges on the abdomen. 



The sutures were also visible on the specimen and are of the usual 

 gastrioceran type. 



Occurrence. — Lower Carboniferous, St. Louis-Chester stage, Bend 

 formation, 5 miles west of Lampasas, Texas. A similar species, thought to 

 be identical with G. entogonmn^ was found by the geological survey of 

 Arkansas in the Lower Carboniferous, Fayetteville shale, near Boles, Ark. 

 Li both Arkansas and Texas this species was associated with Goniatites 

 cumminsi of Hyatt, or Goniatites striatus, according to the writer. 



