Prof. Allman on new Tracheary Arachnidans. 47 



X. — Biological Contributions. By George J. Allman, M.D., 

 F.R.C.S.I., M.R.I.A., Professor of Botany in Trinity College, 

 Dublin, late Demonstrator of Anatomy and Conservator of the 

 Anatomical Museum, T.C.D. 



[With two Plates.] 

 [Continued from p. 9.] 



No. IV. Description of a new Genus and Species of Tracheary 

 Arachnidans *. 



We are indebted to Dr. O'Brien Bellingham of Dublin for the 

 discovery of an Acaroid Arachnidan which he found in consider- 

 able numbers in the posterior nares of a seal {Halichcerus Gry- 

 phus) in July 1837, and which has on examination proved to 

 belong to a form not hitherto described. 



At the Fourteenth Meeting of the British Association held at 

 York in 1844, I noticed Dr. Bellingham' s arachnidan as a new 

 genus and species under the name of Halarachne Halichceri, and 

 under the same designation Mr. Thompson of Belfast has re- 

 corded it in his Report of the Invertebrate Fauna of Ireland. The 

 description there given had been drawn up from specimens not in 

 the best state of preservation, and was necessarily imperfect, but 

 within the last few weeks I have been fortunate enough to obtain, 

 in company with Messrs. Ball and Thompson, fresh examples of the 

 Arachnidan from a specimen of Halichcerus Gryphus taken off the 

 Dublin coast. In the posterior nares of this animal they existed 

 in great abundance v with a species of Ascaris, and thus afforded 

 an opportunity of drawing up a more detailed description of the 

 new genus, to which the following characters may be assigned : — 



Halarachne f. 



Gen. Char. Palps free, filiform ; mandibles didactyle ; sternal 

 lip bifid. Leys with the last joint terminated by two hooks 

 and an intermediate three-lobed caruncle. Body entire, elon- 

 gated, subcylindrical, furnished anteriorly with a dorsal plate. 

 Eyes none. 



Species unica, H. Halichceri. PI. II., III. 



Hob. Infesting the posterior nares of Halichcerus Gryphus, 

 Dublin coast, Dr. Belling ham. 



Halarachne Halichceri measures about an eighth of an inch in 

 length. The abdomen, which presents no trace of distinction 

 from the cephalothorax, is of a somewhat cylindrical form, 



* Read before the Royal Irish Academy, April 12, 1847. 

 f From a\s, the sea, and dpdxvr], a spider. 



