Nigerian Eocene Mollusca. 101 



Family TEREDINID^E. 

 Teredo, sp. 



PLATE n, figs. 6-8. 



REMARKS. Masses of closely arranged Teredo tubes in a woody material, 

 occur in a hard, siliceo-calcareous, reddish brown, ferruginous -looking rock, 

 forming nodules. The outer crust of these nodules consist of a heavy, compact, 

 dark -greenish-grey sandstone although weathering a much lighter colour and 

 becoming quite soft and pulverulent, this external softer material containing 

 many fragmentary molluscan remains. The Teredo tubes vary from one to 

 nearly ten millimetres in diameter, besides having a maximum length of more 

 than 60 millimetres. They are often nearly straight, others exhibit a flexuosity, 

 while all possess a more or less tapering growth ; the rounded and bulbiform 

 summits, where the valves are enclosed, being characteristic of this group of 

 shells. The outer surface of the tubes is more or less annulated, and 

 internally there is evidence of some horizontal septa, as well as two apertures, 

 seen at the tapering ends, divided by a diaphragm, indicative of channels for 

 the passage of the siphons. Most of the specimens are highly mineralised, 

 the tubes being lined within by a calcitic layer which forms a remnant of the 

 original shell structure. The valves are rarely preserved in good condition, 

 although a few isolated examples are of interest in yielding generic characters. 

 They possess the usual globular contour and structure of Teredo^ being 

 composed of three divisions or lobes, the central being narrowest and extend- 

 ing from the umbo to well below the ventral border of the laterals, besides 

 being furnished with a posterior, narrow, and concentrically striated margin, 

 otherwise its surface is smooth ; the lateral lobes also present a concentric 

 sculpture. A deeply angulate emargination exists in the anterior region, thus 

 forming a most prominent gape, which is not bridged over by a callosity as 

 in the allied genus Teredina. The valves, likewise, possess a well marked 

 styloid myophore, which is curved, elongate, depresso-concave, and suspended 

 from or apparently forming part of the inwardly curved umbo which initially 

 is more or less tubercled and which in connection with a similarly rounded 

 tubercle (the parietal tubercle) near the ventral border would suggest (as 

 pointed out to me by Dr. Caiman) a rotatory movement of the valves when 

 being used by the animal for boring wood or other material ; the cavity in 

 front of the umbo is bordered by an enamelled callosity, whilst on the 



