90 Description of a new genus of Trochidea. 



lantois, discovered when the ovum was originally examined. 

 Had any new fact been brought to light in this dissection of 

 the foetus, I should always have had great pleasure in ac- 

 knowledging the share which M. Coste had taken in its reve- 

 lation. 



I have only to add the expression of my regret, that M. 

 Coste, in rectifying, by this dissection, an error into which 

 he had fallen by a too hasty perusal of my memoir, should 

 have compelled me to notice another erroneous statement, in 

 reference to the embryology of the kangaroo. He adds, in a 

 note at the conclusion of his description in the 'Comptes 

 Rendus', No. 18, p. 639, 'Le chorion est confondu avec la 

 vesicule ombilicale" 



I would not, by any means, attribute this extraordinary 

 statement to the necessity which M. Coste felt, of saying some- 

 thing about the chorion, after having asserted that he had dis- 

 dissected the ovum, " (Foeuf de kangaroo, qu'il n'avoit point 

 encore examine);" — but would rather suppose that M. Coste, 

 having fallen into that belief, and finding that his notes and 

 figures related only to the foetus, and its appended vesicles, 

 had no other alternative than to suppose that the chorion was 

 blended, (confondu), with the umbilical vesicle. The true 

 condition of the chorion of this ovum, I have, however, de- 

 scribed in the Proceedings of the Zoological Society, for Au- 

 gust, 1837, and it has induced me to modify my opinion of the 

 ovo-viviparity of the Marsupiata, at least of the kangaroo. 

 I have the honor to be, Sir, 



Your obedient Servant, 



Richard Owen. 

 To M. Arago, 



Secret. Perpetuel de TAcademie des Sciences, &c. &c. 



Art. X. Description of a new genus of Trochidea, belonging to the 

 family of Gasteropoda phytophaga. By G. B. Sowerby, Esq. 

 F.L.S. 



The remarkable shell which forms the subject of the follow- 

 ing observations, was brought to this country some years 

 since, by Captain Beechey, but it has been impossible to as- 

 certain where it was found. The specimen from which the 

 description is taken, is in the possession of Thos. Norris, Esq. 

 of Redvales, who has kindly permitted me to draw and de- 

 scribe it. Another specimen, though in very bad condition, 

 is in the possession of Miss Banks, of Leeds. 



