ACXmOCRINID^. 587 



only one to which his description ajsplies, is an Aetinocrinus. The other was 

 made by Austin in 1848 the type of AmjjJioracrinus, and is now known as 

 AmpJio7'acrinus Gilhertsoni (Miller) = Aetinocrinus amphora Portlock, and 

 Melocrinus amjjhora Goldfuss. 



Eoeiner and Hall confounded Amphoracrinus with Agnricocrinus, and Meek 

 and Worthen at first with Doryciinus, but afterwards accepted the genus in 

 its present form. It differs from both genera essentially in the arm struc- 

 ture, as well as in the form and position of the anus ; and they have also 

 laiiformly a second anal plate. 



Amphoracrinus appears to be a somewhat abei'rant form, and has quite 

 frequently three plates above the anal piece. This, however, is found only 

 among the American species, and only in A. divergens and A. viminalis ; 

 Amjjhoracriniis spinobracJiiatics and the three English species always having 

 the usual two plates. This might seem to indicate that the two former are 

 generically distinct, and should be removed to the Batocrinidce, if it were 

 not for the fact that they also have occasionally but two j)lates above the 

 final, and that in their arm structure, as well as in other respects, they agree 

 most closely — even more than A. spinohrachiatus — with the typical form 

 from England, of which we have a most excellent specimen with arms, from 

 Waterford, Ireland. To imderstand the case correctly, it is important to 

 note that the middle plate over the anal, when it does occur, is compara- 

 tively small and cimeate, often barely touching the anal plate ; and we think 

 it not improbable that it really represents a plate of the second row, and is 

 not a true homologue of the middle plate in the Batocrinidse. On the other 

 hand, we must remember that Amphoracrimcs is one of the earliest represen- 

 tatives of the ActinocrinidiE ; and it may be possible that it is a transition 

 form, in which the Actinocrinoid structure has not been as yet persistently 

 established. At any rate, we see no good reason for separating the two 

 forms, even subgenerically. 



Worthen, in the Geol. Rep. of Illinois (Vol. VIII., p. 96, Plate 14, Fig. 8), 

 described a specimen under the name of Amphor-acrinus jerset/ensis, which is 

 interesting as having but four arm-bearing rays, the free parts of the anterior 

 ray evidently having been destroyed during the life of the animal, and the 

 break closed by abnormal growth. The specimen is too imperfect for a cor- 

 rect diagnosis, and we think it highly probable that it is an Agarieocrinus. 



