P^ECILASMA CRASS A. 107 



3. PiECILASMA CRASSA. PL II. Fig. 3. 



Anatifa crassa. /. E. Gray. Proc. Zoolog. Soc, 1848, p. 44, 

 Annulosa, Tab. iii, figs. 5, 6. 



P. valvis 5; camice termino basali in discum par- 

 vum infossum producto : scutis converts, dentibus inter nis 

 umbonalibus mdlis: tergis {XEne rudimentalibus, vice carina 

 latioribus. 



Valves 5 ; carina with the basal end produced into a 

 small imbedded disc; scuta convex, without internal 

 umbonal teeth; terga almost rudimentary, scarcely broader 

 than the carina. 



Spines on the segments of the posterior cirri arranged 

 in single transverse rows. 



Madeira; attached to the Homola Cuvierii, Rev. R. T. Lowe. British 

 Museum.* 



General Appearance. — Capitulum highly bullate, or 

 thick. Valves rather thick, opaque, either pale or dark 

 flesh-red, smooth, yet rather plainly striated from the 

 umbones. There are a few very minute spines on the 

 membranous borders of the valves. 



Scuta highly convex, broadly oval, apex broad rounded; 

 basal margin narrow, much curved; no internal, um- 

 bonal teeth ; basal internal rim strong, running up part 

 of the occludent margin. A slightly prominent ridge, 

 either rounded or angular, but in one specimen a 

 narrow depressed fissure-like line, runs parallel to the 

 occludent margin and ends near the apex in a slight 

 notch ; this fact is of interest in relation to the structure 

 of the scuta in P. eburnea and P.Jlssa. The scuta are 

 either equally or very unequally convex; in the latter case, 

 the occludent margin of one valve is curled, so that its 

 umbo is not quite medial. 



* It is stated, in ' Zoolog. Proc./ (1848, p. 44,) that this species was 

 attached to a gorgonia, from Madeira ; I cannot but suspect that there 

 has been some confusion with the Oxynaspis celata from Madeira, which is 

 thus attached. 



