THE SESSILE BARNACLES. 257 



TETRACLITA SQUAMOSA MILLEPOROSA, new subspecies. 

 Plate 60, figs. 1 to Id. 



Type.G^i. No. 58059, U.S.N.M., from Albemarle Island, Gala- 

 pagos. 



The form is often lower, more spreading than usual, the orifice 

 very small. External lamina wholly eroded, exposing the fine, short, 

 scalelike upfilled pores ; sutures usually wholly obliterated externally, 

 calcified. Walls very thick, the pores very small and numerous. Ex- 

 ternal color ivory yellow or with a grayish tone, the sheath dark 

 varley's gray or violet-slate. Diameter 46 mm., height 16^ mm. 



The opercular valves are very small. Scutum short and broad, 

 white within, stained with dull purple on the articular rib and at the 

 base of the occludent margin. Articular rib not so strong as in sta- 

 lactifera. Adductor ridge strong, parallel to the rounded basitergal 

 border, approaching the articular ridge above, and separated from it 

 by a superficial groove only. 



The tergum is shaped much like that of T. s. xtalactifem, the spur 

 being wide with oblique end; but the carinal side of the valve is 

 somewhat narrower than stalactifera, the scutal side wider. 



Related to panamensis by the unusually thick wall, which is so calci- 

 fied that it can not be broken along the sutures; but the tergum is 

 shaped like that of stalactifera. 



TETRACLITA SQUAMOSA RUBESCENS Darwin. 



Plate 61, figs. 1 to le. 



1854. Tetraclita porosa var. rubcscens DARWIN, Monograph, p. 329, pi. 10, 



fig. 1& (? and I/, 1m). 

 1854. Tetraclita porosa var. elcgans DARWIN, Monograph, p. 330, pi. 10, 



fig. Id. 



Distribution. Farallones, California, to Cape St. Lucas, Lower 

 California. 



The surface is dull, eroded, roughened like thatch, varying from 

 deep hellebore red to livid brown, sometimes with a gray-white zone 

 at the base, where it is less deeply eroded in some specimens ; sheath 

 colored like the exterior. The pores are larger than in typical squa- 

 mosa. 



Scutum but little cut oil at the basitergal angle, and with the 

 adductor ridge strongly developed; white below the adductor ridge, 

 corinthian purple or deep hellebore red above it. The occludent mar- 

 gin has only one to three very long, very oblique teeth. 



Tergum is extremely narrow, its greatest width but little exceed- 

 ing one-third of the length ; carinal part of the base steeply sloping, 

 nearly in line with the adjacent border of the long spur. Crests for 

 the depressor muscles strongly developed. Corinthian red, fading to 

 white at end of the spur. 



