ZOOLOGY. 359 



GASTROPTERON AND ITS RELATIONS. 



A remarkable form of gastropod mollusk, which was at one time su])- 

 ])osed to be a Pteropod, has now been well ascertained to be a Tec.ti- 

 branchiate and most closely related to the Bnllidea. In general form it 

 has, in fact, considerable resemblance to a Pteropod, and the shell is so 

 small and immersed that it was not detected until Krohn found it in 

 ISliO. The shell resembles somewhat that of a Carinaria in form, and is 

 quite translucent: it is found in the hepatic region near and somewhat 

 behind, but a little to the right side of, the anus. 



Mr. Vayssiere has investigated the anatomy of this form, and has 

 reached, in respect to its relation, some conclusions dilfering from his 

 predecessors.* He regards Gastropterori as the type of one of two major 

 groups, into which he would divide the Bullidea, most of the forms of 

 that type constituting the second group. 



In this first group represented by Gastropteron the parapodia are 

 largely developed : a small nautiloid shell is contained within the 

 mantle; and the (esophageal collar is constituted by a pair of cerebral 

 ganglia, a i)air of pedal ones, and six visceral ones; the visceral ganglia 

 are distributed in equal number, three to the right and three to the left. 



In the second division the parapodia are rudimentary ; the shell well 

 developed.and generally external; and there are only three visceral 

 ganglia, two of which are on the right and one on the left side. 



It is observed also that Avhile in Gastropteron the genital nerve arises 

 directly from the counnissure without the intermediation of any gan- 

 glionic enlargement, in the other forms the corresponding nerve always 

 arises from the larger of the two left ^'isceral ganglia. 



LIVING PLEUROTOMAEIIDS. 



Among the most interesting of the mollusks is the genus Phuroto- 

 maria. This genus was for a long time sui)posed to have become entirely 

 extinct, but in 1850 a species was discovered at the island of Guade- 

 loupe and named by Pischerand UernardiP/t'«ro/ow<(r/« (Juoi/ana, Sub- 

 sequently a specimen of a second species was also obtained and described 

 under the name of Fleurotomaria Adansoniana in 1801. In 1880 further 

 information respecting the development of the genus Avas obtained. A 

 second i^\)Qxt,h\ie\iof Fleurotomaria Adansoniana (1>1 millimeters wide) was 

 found in the " grand cul de sac de la Point-a-Pitre," Guadeloupe, at a 

 dei)th of 150 fathoms, and two new species were obtained in the Eastern 

 seas. One has been descril)ed by Hilgeudorf as I'leurotomaria Beyriehii, 

 Irom a specimen obtained in Jajiau. Another has been made known as 

 Fleurotomaria Rumpfii by Schei)man, and the specimen on which it was 

 based (a very large one, having a maximum diameter of 190 millimeters) 

 way found in a collection of shells from the Molucca Islands belongiug 



* Vayssiere. Eechercbes iinatomiiiiies sur les moUubiiues dc lii lamille des BuUides. 

 Ann. So. Nat., Zool., (0,) vol. ix, No. 1 (G4 i>p., 3 pi.). 



