14 PEOCEEDIlSrGS OF THE NATIONAL MUSEUM vol.78 



2. ON THE ONYCHOPHORAN AYSHEAIA PEDUNCULATA WALCOTT 



In his contribution dealing with the extraordinary annelid fauna 

 of the Burgess Shale, Walcott (1911) described among other new 

 forms a unique specimen which he named Aysheaia pedunculata, 

 placing it as a polychaet in a new family the Aysheaidae. The 

 remarkable resemblance of this fossil, as illustrated by Walcott, 

 to the living Onychophora could not fail to impress itself on 

 anyone familiar with the recent members of the group. Aysheaia 

 has therefore been placed in or near the Onychophora by various 

 authors since it was first made known (Brues 1923, Handlirsch, 1925, 

 1926, Walton, 1927), but no further details of its structure have 

 hitherto been published. 



While examining the specimens of OpaMnia described above, it 

 seemed probable that a reinvestigation of Aysheaia w^ould be profit- 

 able in the hope that any relationship it bears to the living Onycho- 

 phora might be more certainly determined. 



Type specimen. — The type of Aysheaia pedunculata consists of 

 a very distinct worm-like fossil, 31 mm. long, lying on a piece of 

 shale near a well preserved example of the problematic worm Ottoia 

 prolifca Walcott. On the same slab are fragmentary remains of 

 MarreUa and other animals. A reverse specimen of that part of 

 the slab bearing the type of Aysheaia also exists in the collection. 

 The left side of the worm is probably perfect and shows at least 

 10 pairs of appendages. The posterior region on this side is 

 rather confused, but it is highly probable that an eleventh append- 

 age is lying close up against the tenth w^hich is otherwise unaccount- 

 ably thick. Most of the right margin behind the fifth appendage 

 is missing. Walcott describes the anterior end of the animal as 

 forming a head which is said to consist of '' a central narrow longi- 

 tudinal section — a rounded lobe on each side of its posterior half 

 that suggests large eyes; the anterior end appears to have short 

 slender tentacles projecting forward." On examining the type I 

 was suprised to find that this head is very ill defined, and composed 

 of a material of different texture to that of the rest of the fossil. 

 The boundaries of the parts are very obscure, and seeing that there 

 is absolutely no trace of such a structure in any of the undescribed 

 material, much of which is in very perfect condition, it is probably 

 either a piece of prolapsed alimentary canal, or a decayed fragment 

 of one of the verj- numerous organisms associated with Aysheaia 

 in the same slab of shale. It is unnecessary to describe the other 

 features of this specimen here as their true nature will become 

 apparent when viewed in the light of the better preserved additional 

 material. 



Additional specimens of Aysheaia pedunculata. — The collections 

 made by AValcott subsequent to the publication of his preliminary 



