On the Morphology and Classification of the Saleriiidse, 117 



neck ; posteriorly the thin edges are turned over the back. 

 Creamy white in colour. The posterior is twice as large 

 as the anterior sucker, is quite circular, prominent, 1 inillim, 

 in diameter J it is placed just anteriorly to the middle of the 

 ventral surface. 



The pharynx is large, and cseca are developed from the 

 hinder halves only of the two branches of the intestine. 



The eggs are scattered abundantly through all but the 

 anterior region of the body, and call to mind the figure given 

 by Olfers of Distomwn folium^ from which species (found in 

 the urinary bladder oi Esox lucius) this may be at once distin- 

 guished by the absence of a neck; the eggs measure 0*1065 

 millim. in length, and '07 millim. in breadth. 



The length of the whole body is 5*5 millim., and its greatest 

 breadth 3 millim. 



The specimen of Halosaurus from which this fluke was 

 taken was dredged off Cape St. Vincent at a depth of 

 1090 fathoms. 



XV. — On some Points in the Morphology and Classification 

 of the Saleniidge, Agassiz. By Prof. P. Maetin Duncan, 

 M.B., F.R.S., F.L.S., and W. Percy Sladen, F.G.S., 

 Sec. L.S. 



Contents. 



The Sur-anal or Dorso-central Plate and its Homologies ; the Periproctal 

 Plates. Some new Points about the Genera Acrosalenia, Peltastes, 

 and Salenia, and a reconsideration of the Classificatory Value of the 

 Genera Fseudosalenia, Hyposalenia, Ooniophorus, and Heterosalenia. 



I. The Sur-anal Plate. 



When the genus Salenia is mentioned, or the family of the 

 Saleniidse, to which it belongs, one of the most important 

 structures inevitably arises in the mind — the sur-anal plate, 

 with its many synonyms. The term has been an unfortunate 

 one, although nothing could have been clearer than the 

 meaning which its author desired to give it. L. Agassiz 

 wrote, in his Monogr. d'fichinod. Viv. et Foss., 1838, livr. i. 

 p. 6 : — " The genus Salenia^ restricted within the limits now 

 assigned, is characterized by an odd plate placed in the 

 midst of the oviducal apparatus, which I shall call the sur- 

 anal, which, consequent on its position vis-a-vis to the anal 

 aperture, always renders the anus excentric." 



