OP SOUTHERN INDIA. 13 



from those of the psoladin^. Each valve has a distinct anterior auricle, while 

 the posterior is visually also separated from the central hody hy a special groove. 

 This body, or the middle area of the valve, is itself again often divided by a median 

 ridge into an anterior (generally smaller) and a posterior area, the imbrication on 

 both converging towards the central ridge running from the apex to the periphery, 

 and here, in the middle of the ventral region, usually terminating with a small 

 solid boss. The form of the valves greatly varies with the age of the specimens, 

 the shells having, when young, the umbones perfect, while with progressive growth 

 the entire upper portions of the shell become more or less corroded. In the same 

 way the front portion of the anterior auricle is liable to great changes, bein"- an 

 essential part of the shell employed in the boring operations of the animal. In the 

 form of the tubes there are also numerous variations to be observed. It is evident 

 that, when the anterior end of the tube is closed, the animal can only effect its 

 progress in boring when it has dissolved the frontal diaphragm ; this must lead us 

 to suppose that the Teredos bore only at certain times of the year, while at other 

 times ( ? the breeding or hatching season) they are at rest, the tube being closed 

 anteriorly. 



The following are the principal generic groups, as partially suggested by 

 Dr. Wright:— 



1. Teredo, Sell., 1732. Palettes testaceous, single, oblong, usually truncate at 

 the end; tubes long, gradually increasing {T. norvegica, Spengl.). 



2. TJperotis, Guett., 177i. Palettes testaceous, spoon-shaped, dej)ressed ; 

 tubes short, club-shaped (Z7. clava, Gmel.). 



3. Kiiphus, Guett., 1771. Palettes testaceous, club-shaped, with the ends 

 expanded and truncated, spatulate, {Kiqjh. Mannii, Wright). 



4. Calohates, Gould, 1862. Palettes dilated towards the middle, with a nar- 

 rower spoon-shaped and long process at the end ; the basal j)rolongations of the 

 palettes are bony, (C thoracites, Gould). 



5. Nansitoria, Wright, 1861. Palettes testaceous, solid, elongated and pyra- 

 midal, flattened inside, transversally imbricated on the outer convex surface, 

 ( JV. Dun Zop w, W r i g h t) . 



6. Xylotrya, Leach, 1810, (teste. Gray). Palettes very long, more or less 

 bony or horny, with lateral flexible serrations or setse, (X. hipinnata, Turt.). 



? 7. TeredoUtes, Desh., 1S12, (Mem. Soc. Geol. do la France, vol. v, p. 2). 

 This was proposed by Deshayes for a cretaceous species, T. clavatus, known only 

 by some tubes which are short, clavate, and in position, as they occur in the rock or 

 wood, almost parallel to each other. Deshayes does not take any notice of 

 this supposed new generic type in his subsequent revisions of the Fkolabid^, 

 but the form of the tubes is certainly very peculiar, and it is very likely that the 

 animals were somewhat different from those of Teredo. Martesia and Parapholas 

 bore in wood in a way very similar to this fossil form, which ought to be carefully 

 compared with them. 



D 



