542 BULLETIN 100, UNITED STATES NATIONAL MUSEUM 



TEREDO (TEREDOTHYRA) RADCLIFFEI, new species 

 RADCLIFFE'S SHIPWORM 



Plate 53, figs. 11, 14; plate 56, fig. 5; plate 59, figs. 7, 8, 9 



Shell small, thin, semitransluscent; the extreme anterior portion 

 of the anterior part forms a narrow sinus which is covered by a 

 rather thick callus that is partly reflected over the outside; the rest 

 of the anterior part is covered by numerous slender, closely spaced 

 denticulated ridges, of which 72 are present, and many more must 

 have been lost when the apices of the umbones were eroded. These 

 denticulated ridges become fused at the anterior margin and are sepa.- 

 rated on the early part of the shell by spaces about twice as wide as 

 the ridges, and on the later portion by spaces about as wide as the 

 ridges at their posterior extremity. Their free margin is finely den- 

 ticulated; the anterior median area is very broad and marked by 

 numerous ridges that bear strong denticles. Of these ridges 44 are 

 present in a line projected across the area from the ventral border of 

 the" anterior part. The denticles are exceedingly fine. The middle 

 portion of the median area is rather broad and crossed by the dis- 

 tantly spaced, outbent continuations of the dental ridges, which here 

 lose their denticles, and fine lines between them. There are also two 

 rather strong radiating lines present. The posterior portion of the 

 middle part is about as wide as the anterior and middle portion com- 

 bined, and is marked by the decidedly upbent continuations of the 

 lines already referred to for the middle part. The posterior part 

 forms a narrow auricle which is conspicuously constricted off where 

 it joins the posterior portion of the median part. Interior of the 

 shell bluish-white. A strong suture marks the junction of the ante- 

 rior and middle part; there is a rough area marking the middle por- 

 tion of the middle part bearing a conspicuous knob at its ventral 

 margin. The posterior part extends over the posterior portion of 

 the middle part as a shelf which is spatulate in shape, the narrowed 

 handle extending up to the umbonal knob. There is a deep cavity 

 behind this shelf. A slender thin blade extends from under the um- 

 bone obliquely ventrally through about two-thirds of the shell. The 

 pallets are long and spatulate, the stalk occupying about two-fifths 

 of the length. The expanded portion extends as a narrow wing down 

 the two sides of the stalk; the distal portion of the pallet is deeply 

 impressed to form the two pits, and there is an excavation on the 

 two lateral margins where the calcareous and horny portions join. 

 On the inside the pallets show the continuation of the stalk to almost 

 the distal portion of the calcareous part, the lateral wings of the pal- 

 let being concave on each side. The horny portion has two lateral 

 horns. 



