DESCRIPTIONS OF SPECIES. 



85 



with forma of Platytrochus, but it does not possess the broad marginal costse 

 nor the cohimeHa characteristic of that genus. 



Mihie-Edwards and Haime, from Lea's figure, considered the species 

 very close to Sphenotrochm' miUetianus (Defrance). From the figure of Sp. 

 milletianus, given by Michelin,' the two forms appear very distinct. The sides 

 of Sp. miUetianus, at the end of the longer transverse axis, are subi)arallel ; the 

 corallum may possibly be narrower at the calicular margin. The sides of 

 Sj). nanus, however, taper to the base. 



SpHENOTROCHUS CLAIBORNENSIS Sp. nOV. 



PI. VI, figs. 1 to 3a; PL V, fig. 22 (?). 

 Corallum cuneiform; cross section compressed elUptical; base rather 

 narrow or quite wide, but in the latter case narrower than the length of the 

 ffreater transverse diameter of the calice. In the base a sand grain is some- 

 times included. Measurements of four specimens give the following: 



Greater diameter of caliee . 

 Lesser diameter of calice . . 

 Heigbt of corallum 



Mm. 

 3.75 



Mm. 

 4.5 

 2.3 

 6 



Mm. 

 5 



2.5 

 7.5 



The calicular margin is considerably lower at the ends of the longer 

 transverse axis than at the ends of the shorter. The two costse, one at each 

 end of the longer transverse axis, and the costse standing immediately next 

 these two — six in all— are wider than the others, and are densely granulate. 

 The other costaj are narrow, and are simple costal plates, or may be in part 

 a sino-le row of granules, or may be partly composed of a double row of 

 granules. All three conditions are represented. The mode of costal develop- 

 ment is identical with that already described for Sphenotrochus nanus, i. e., 

 new costiB are introduced at only four points, on each side of the costse 

 standing next the costse at the ends of the shorter transverse axis of the 

 corallum. The costce con-espond to the septa. There are 40 septa in speci- 

 men No. 3 of the above table of measurements; ui specimen No. 4 there 

 are 36. Very many of the septa reach the columella. The upper margins 



' Iconographie Zoophytologique, pi. Ixxiv, fig. 1. 



