OCR Text |
Show 428 PROF. F. J. BELL ON THE TEMNOPLEURIDAE. [Julie 1, 1. SALMACIS BICOLOR, Ag. Salmacis bicolor, Agassiz and Desor, Cat. Rais., Ann. Sc. Nat. (3) vi. p. 359. This, when completely covered with spines, is a most beautiful form : above the ambitus it is covered with short sharp purplish red spines, banded with greenish-yellow ; at aud below the ambitus the spines are much stronger and longer and are more closely packed, while the colours are reversed in relation, and they may be said to he of a greenish-yellow, banded with a purplish red; the base, however, is always coloured red. Around the actinostome the spines are still stronger and are completely flattened. The test is well rounded and by no means conical. The actinal and abactinal areae are of a moderate size ; a bare median space can, above the ambitus, be distinctly made out in both the ambulacral and interambulacral areae. In the denuded test the primary tubercles on the interambulacral plates are, above the ambitus, best developed on the half oi the plate nearest the ambulacral pores ; about the middle of the side of the test there are two well developed primary tubercles, and internally to these there are two smaller ones; passing upwards these latter gradually diminish in size till they disappear ; and within a few plates of the abactinal area the same happens with the outermost row of tubercles; so that the uppermost of the coronal plates have only one well-developed primary tubercle each. At the ambitus there are five well-developed primary tubercles on each interambulacral plate ; and these tubercles, forming a close mail on the actinal face of the test, gradually disappear as they pass towards the actinostome. There is a fairly well-marked series of miliary tubercles running along the upper edge of each coronal plate; but these become much more irregular on the uppermost plates. A dark-coloured band runs along the sutures of the plates above the ambitus. On the ambulacral plates the primary tubercles form a single row, which is placed quite at the outer edge and extends regularly from pole to pole, gradually decreasing in size as they pass in either direction from the region of the ambitus ; it is only quite close to the ambitus that a second row of primary tubercles is at all well-developed. The actinostome is of a moderate size, not sunken ; its decagonal form is well marked, the ridges connecting the auricles are low ; the pore-areas are wide, four pores, or two pairs, being placed in an almost horizontal line. The sutural pores appear to become indistinct with age. i ii iii Absolute diameter in millims. 44 52 75 Percentage value of Height. 59 596 66-6 Abactinal area. 18 1739 16 Anal area. 8 Actinostome. 29-5 27-8 24 Poriferous zone. 2 2-6 3 |