31.S 



3. First Steps towards a Monograph of the Recent 



Species of Petaloconchus, a Genus of Vermetid^. 



By Philip P. Carpenter. 



Genus Petaloconchus, Lea. 



H. C. Lea, Trans. Am. Phil. Soc. 1843, vol. ix. p. 229 ; Woodw. 

 Man. Moli. pt. iii. p. 4&2 ; B. M. Cat. Mazatlan Moli. p. 308. 



Animal ignotum. 



Operculum (speciebus ii.) parvum, cornenm, diaphanum, tenuis- 

 simum, pariim concavum ; cicatrice centrali ; anfractihus paucis, 

 cix apparentibus. 



Testą extns Bivonise similis ; intu» fransversim rarissime sep- 

 tata ; anfractihus medianis laminis elonyatis spiralibus varie dispo- 

 sitis, cameram scepe pcene secantibus ; plerumųue duabus, plica 

 columellari una. 



Hab. Mare jMediterraneum ; Oceanum Atlanticum, Pacificum, 

 Indicum. 



Shell of corkscrew gro^th, glomerate, or single, affixed by one 

 side of the whirls ; earlier and later whiils open ; middle whirls 

 di\"idcd by spirai laminse, often of complex structure, which gra- 

 dually pass away at each end ; generally two, nearly meeting, ^^•ith 

 a third rudimentary, forming a columellar plait. 



The eliraiuation of the species is a work requiring great care ; as 

 some outside exactly resemble certain species of Bivonia ; and as 

 the intemal structure varies according to the position in which the 

 shell is broken, a few whorls often altering the character rery deci- 

 dedly. The structure was first observed by Lea in fossil species ; 

 it was not noticed, howeTer, in subsequent works till the publication 

 of the third part of Ayoodward's Manual. In the mean time, having 

 carefully observed the structure in the Mazatlan species, Dr. Gray 

 kindly allowed me to examine the specimens in the British Museum 

 collection, and Mr. Cuming entnisted to my care the suspected 

 specimens among his invaluable stores. The result of these inqui- 

 ries is now offered, simply as a provisional introduction to the sub- 

 ject ; in the hope that those who have the means of lapng open 

 specimens from top to bottom will do so, and especially that those 

 who have access to them iu a living statė will inąuire what pecu- 

 liarity in the animal is co-ordinate with so remarkable a structure 

 in the shell. 



A. Laminis ab axi procedentibus. 



I. Petaloconchus macrophragma, n. s. (fig. 1.) 



B. M. Mazatlan Cat. no. 359. p. 309. 



P. t. parva, dextrali, dense purpureo-fusca ; cijlindracea, solute 

 spirali, niarginibus spirte stepe subparallelis ; plerumrpie ylome- 

 rante, interdum solitaria ; basi ad conchas, seti altera ad al- 

 feram, constricte adheerente, scepe erodente ; superfcie rugis 



