114 University of Texas Bulletin 



very rare at Tsan-tien in China. Wanner found hundreds of Agathi- 

 ceras at Bitaunu on the island of Timor. In the Glass Mountains we 

 have found numerous specimens of Agathiceras in two different strata : 

 the Wolfcamp formation, and the Word formation. In the first one, 

 hundreds of specimens can be collected in a very limited locality, while 

 in the second horizon another species of Agathiceras occurs by the 

 thousand in certain beds. It often nearly covers the surface of some 

 limestone beds. 



Agathiceras Frechi nov. sp 

 PI. V, Fig. 39-54; PI. VI, Fig. 1-26 



Shell discoidal, with somewhat compressed flanks and rounded ven- 

 tral part. Whorls numerous and deeply embracing, cross-section 

 nearly hemispherical in very young individuals, and parabolic in the 

 older ones, the height of the whorl being generally less than the width. 

 The difference is very small in the largest specimens bvxt very great in 

 the smallest ; that is to say, the height grows much more rapidly than 

 the width of the whorl. The greatest width lies a little above the um- 

 bilicus; at this place the surface of the flanks bends down rather 

 abruptly, although in a curve, toward the umbilicus. The umbilicus 

 is nearly closed; in the largest one (No. i of our table of dimensions, 

 pi. V, fig. 39-41) it has a diameter of only i.o mm. so that the ratio 

 to the diameter would be only 0.045. Each whorl shows about four 

 deep constrictions in the larger whorls; in the smaller ones (Nos. IX 

 to XI of the dimensions table below) there are even five, but on the 

 innermost (Nos. XII to XIV) they disappear altogether. They are 

 slightly curved forward on the flanks and backward on the ventral 

 region. The body chamber is unknown. 



On several specimens the shell is preserved and shows the common 

 spiral ornamentation of Agathiceras. In No. XI of our dimension 

 table the spiral ribs are sharp and as broad or even broader than the 

 furrow-like interstices (pi. VI, fig. 9, 14). We count about twenty-six 

 spiral ribs between the umbilicus and the sipho. On No. Ill of ou:" 

 dimension table (pi. V, fig. 49-54) the spiral ribs are very thin and 

 separated by broad and flat interstices ; there are probably not more 

 than thirty ribs between the umbilicus and the sipho. The ribs are 



