Hyatt.] 312 [April 4, 



Celaeceras 1 , nobis, includes only Cel. (Gon.) praematurum, 

 sp. Barr. Syst. Sil. pi. 522. It is unique among Silurian forms in 

 the- sutures, which possess outlines similar to those of the more 

 complicated Devonian and Carboniferous forms. There is in Bar- 

 rande's figures, though not described by him, ventral saddles, 

 similar to the saddles of Pinnacites and on either side are two 

 deep lateral lobes similar to those of Glyphioceras. The first pair 

 of lateral saddles are large and hastate, and the second pair of 

 lateral saddles broad and rising rapidly to the umbilicus. 

 The shell is not very involute, showing that it is a member of a 

 larger series, which probably had both less involute and also pos- 

 sibly some more involute members. The inner lateral saddles as- 

 sociate it with the Agoniatites rather than Anarcestes. We re- 

 gard it as having probably the same relations to Agoniatites, that 

 Heminautilinus has to Anarcestes. The young, as in Heminautil- 

 inus, will probably be found to repeat the parent form until a late 

 larval stage in some species. M. Barrande repeatedly alludes to 

 this species as one of his best illustrations of anachronic species, or 

 species which are out of place in time ; which more closely resem- 

 ble succeeding forms of more complicated structure than those 

 of the fauna in which they occur. To us they are simply highly 

 specialized forms, which have adopted habits similar to those of 

 the species they resemble, and have been accordingly modified in 

 their adolescent and adult stages, but still retain in their larval 

 and adolescent stages the marks of their recent origin from the 

 lower forms with which they are associated. We have accord- 

 ingly named this form, the racer 



[Note.] 

 CLYMENINAE 



This group has characteristics which are so evenly balanced that we should have 

 found it difficult to decide whether it was Nautiloid or Aramonoid, if it had not 

 been for the protoconch, and the young sutures, which are shown by Branco in the 

 Paleontogr. Vol. 3, 1880, pi. 8, fig. 1. The sutures in the young have ventral lobes, 

 and the broad ventral saddles of the group are developed later. It is, therefore, an 

 Ammonoid, but we cannot say that the young resemble the lower GoniatiteSj since the 

 first suture of the only species known, in place of being asellate, or straight, has a 

 broad saddle as in the higher Goniatites. A still more remarkable peculiarity, if gen- 

 eral, is, as stated by Branco the absence of depressions on either side of the neck of 



■ KtXns, a racer. 



