SS* FOURTH REPORT — 1834. 



its surface. As these striae, however, have been used in some 

 cases for characterizing the genera of the Pectinibranchiate 

 Gasteropoda, this memoir is not without its importance to the 

 systematist. During the last year Mr. Gray has again turned 

 his attention to this subject. In a paper in the Phil. Trans. 

 for 1833, he has detailed some observations on the structure of 

 the part in question, as well as on the structure and oeconomy 

 of shells in general. He considers that the mere fact of the pre- 

 sence or absence of the opercle is of small importance, but that 

 in its form and structure it offers some of the most constant 

 characters for the distmction and arrangement of families and 

 genera. 



4. Brachiopoda. — Mr. Owen has recently published * an im- 

 portant memoir on the anatomy of this group, in which he has 

 offered some remarks with respect to its value and affinities. 

 He observes that in all essential points of structure these ani- 

 mals closely correspond with the Acephalous Molliisca, al- 

 though inferior to the Lamellihranchia as far as regards their 

 respiratory and vascular systems. He considers them as hold- 

 ing a middle place between these last and the Timicata; not, 

 however, possessing characters of sufficient importance to justify 

 their being regarded as a distinct class, but forming a separate 

 group of equal value with those above mentioned. 



5. Tunicata. — Whether we admit this group as a class or 

 only as an order, it is one which will always possess interest as 

 affording a natural passage to the Radiatn of Cuvier. It is 

 especially to the researches of the naturalist just mentioned, and 

 to those of Savigny, that we are indebted for the first accurate 

 knowledge obtained respecting these animals. While the struc- 

 ture of the simple Tunicata was beautifully illustrated by the 

 dissections of the former t, the latter had the merit of discover- 

 ing the true organization of those singular compound AscidicB 

 which until his time had always been confounded with the 

 zoophj-tes %. Peron, Desmarest, and Lesueur have all likewise 

 contributed to render this group better understood. What re- 

 cent additions have been made to our knowledge of it are 

 due principally to Mr. MacLeay, MM. Quoy and Gaimard, 

 MM. Audouin and Edwards, and Dr. Meyen. Mr. MacLeay is 

 the author of a paper, read to the Linnaean Society in 1824 §, in 

 which he has given the anatomical details of some new forms 

 from the Northern seas, at the same time that he has thrown 



• Zool. Tram. 1834, vol. i. p. 145. 



f See Ann. du Miis., torn, iv., and Mem. du Mus., torn. ii. p. 10. 



X Mem. sur les An. sans Verieb., Part 2. 



§ See Linn. Trans., torn. xiv. p. 527. 



