176 TEREDINID.E. 



4. T. mego'tara*, Hanley. 



T. megoiara F. & H. i. p. 77, pi. iv. f. C, and xvii. f. 1,2. 



BoDT pale bluish -white : mantle not very thin : foot mus- 

 cular and coriaceous, attached by a thick and powerful cylin- 

 drical stalk (Clark). 



Shell convex, soUd, opaque, and rather glossy, parted in 

 the middle by a slight longitudinal crest, with a very broad 

 but shallow furrow on the posterior side : sculpture divided 

 into four distinct portions, viz. anterior, middle, furrowed, 

 and posterior : the anterior consists of sharp, narrow, and fine 

 transverse plates from 25 to 30 in number, which are more 

 remote at first and become closer at advanced periods of 

 growth ; the edges of these plates are microscopically notched 

 across; this portion represents a triangle having an acute 

 apex at the back of the valve and a broad and nearly straight 

 base : the middle portion extends the whole length of the shell 

 and is strip-like, the upper part Ij'ing between the inner line 

 of the anterior area and the crest which separates one side 

 from the other, and the lower part being open outside and 

 bounded by the crest on the inner side ; the broadest part is 

 at the point of the angle where the anterior and middle por- 

 tions join ; this middle portion consists of 15-20 extremely 

 delicate and nearly equal striae, the outermost of which are 

 exquisitely beaded, and the inner rows strongly but closely 

 notched across ; these striae are longitudinal, ^vith an oblique 

 tendency towards the posterior side, and they diverge from the 

 transverse striae at a right angle : the furrowed portion is 

 marked with curved but not much raised transverse steps, 

 which gradually widen as they approach the front or ventral 

 edge : and the posterior portion is almost smooth or only 

 marked near the furrow by indistinct lines which form a con- 

 tinuation of the steps above mentioned : colour milk-white : 

 epidermis membranous, creamcolour, more persistent on the 

 anterior area : margiiis acutely angular on the upper part of 

 the anterior side, with a large triangular excision on the lower 

 part, so that when the valves are united the opening or gape 

 is broadly heart-shaped ; they are bluntly pointed or rounded 

 in front, and incurved on the posterior side, which is termi- 

 nated by a large compressed and rounded ear- shaped expan- 



* Great -eared. 



