ZOOLOGY. 359 



GASTROPTERON AND ITS RELATIONS. 



A remarkable form of gastropod mollusk, which was at one time sup- 

 posed to be a Pteroi>od, has uow been well ascertained to be a Tecti- 

 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 Krohu found it in 

 1800. 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 Gtustropteron 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 groui). 



In this tirst group represented by Gastropteron the parapodia are 

 largely develoi)ed : a small uautiloid shell is contained within the 

 mantle; and the €esoi)liageal collar is constituted b}^ a i>air of cerebral 

 ganglia, a pair of pedal ones, and six visceral ones; the visceral ganglia 

 are distributed in c<]ual 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 oidy 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 

 direct];^ from the coumiissure without the intermediation of any gau- 

 gliouic enhirgement, in the other forms the corresponding nerve always 

 arises from the larger of the two left visceral ganglia. 



LIVING PLEUKOTOMARIIDS. 



Amoug the most interesting of the mollusks is the genus Pleuroto- 

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

 extinct, but iu 185G a species was discovered at the island of Guade- 

 loupe and named by Fischer and l^iiviidvyiiricurotomaria (Juoyana. Sub- 

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

 under the name of Fleurototnaria Adannoniana in 18G1. In 1880 further 

 information respecting the development of the genus was obtained. A 

 second specimen of P/eMroto?»ttria Adansoniana (91 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 si)ecies were obtained in the Eastern 

 seas. One has been described by Hilgendorf as Pleurotomaria JJeijrichii, 

 Irom a specimen obtained iu Jai)an. Another has been made known as 

 Flvurotomaria Rumpjii by Schepmau, and the si)ecimen on which it was 

 based (a very large one, having a maximum diameter of 100 millimeters) 

 was found iu a collection of shells from the Molucca Islands belougiug 



* Vayssiere. Eeehcrclies £iuatomi(juea sur les mollusques tie la famille dea Bullides. 

 Ann. Sv. JS'at., ZooL, (0,) vol. ix, No. 1 (G4 pp., 3 pi.). 



