238 



PROCEEDINGS OF THE ACADEMY OF 



[May, 



(except for acceleration) with those of some of the Texas Lower Clai- 

 borne races of A. petrosa. In this particular respect A. clayi more 

 closely resembles all the races of A. petrosa than it does A. sayana. 



Athleta clayi is similar, then, to A. petrosa in its later stages, but similar 

 to A. sayana in its smooth and curved rib stages. ^^ It may be reason- 



Fi 



Fig. 3. 



Fig. 4. 



Fig. .5. 



3. — Apex of Athleta petrosa Con. St. Maurice, Louisiana. Showing the small 

 first whori and the relatively long smooth stage. In whorl 3 the curved ribs 

 are seen passing into the tubercled ribs of the cancellated stage. Length 

 about .75 mm. 

 Fig. 4. — Apex of Athleta clayi. St. Maurice, Louisiana. Shows the large and 

 smooth first whorl. The tubercled ribs of the cancellated stage are displayed 

 in whorl 2. Length about .8 mm. 



o. — Apex of Athleta sayana Con. Claiborne, Alabama. Shows the large smooth 

 whorl and the smooth stage which is restricted to a little over one whorl. 

 Li whorl 2 the almost suppressed curved ribs are seen passing into the 

 tubercled ribs of the cancellated stage. Length = 1.8 mm. 



Fig. 



ably regarded as an intermediate between the Athleta petrosa main 

 stock and Athleta sayana. \ 



One more ciuestion is worth considering before we leave the discus- 

 sion of the morphology. Wliat is the meaning of this restriction of the 

 smooth stage to a little over one whorl ? If the size of the apex remained 

 the same it would be best explained as an example of acceleration. 

 The size of the first whorl, however, is not the same as in Athleta 

 petrosa, but is larger in A. clayi and still larger in A. sayana. May not 

 this change then represent only an enlargement of the veliger, rather 

 than a case of true acceleration? The wTiter feels that with present 

 data he is unable to solve this particular part of the problem. Though 



'^ The author realizes perfectly that the proprietj^ of separating .4 . claiji from 

 .4. petrosa may be questioned by some workers. Those who object to his 

 arrangement will probably bring up the frequently cited case of Sturany's Fusus 

 bijrons (Gastropoden des Rothen Meeres). Judging from the figures it would 

 seem, however, that Sturany is dealing with what would be regarded by most 

 sj'stematists as two distinct species. 



