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Show 1880.] PROF. F. J. B E L L O N T H E T E M N O P L E U R I D A E . 439 For the purpose of this investigation it is unnecessary to enter into a detailed comparison of the two admirable sets of figures of A. formosus and A. pallidus given by Valenciennes ill the plates to the ' Voyage de la ' Venus,' *' for there is no question as to the existence of two very different forms ; the difficulty lies rather in the presence of intermediate forms. Thus both Valenciennes and Agassiz would seem to look upon the rarer sutural pores of A. pallidus as an important distinction ; but specimens, and those always small, will be found in which these pores are just as numerous as in A. formosus ; and, on the other hand, there may be found examples of A. formosus in which the sutural pores are just as rare as in the typical A. pallidus. Again, although they are rare, secondaries and miliaries are to be found in the poriferous zones oi A. formosus, and may be rare enough in A. pallidus. I am, on the whole, inclined to keep these two species distinct; the differences in proportion are differences which, if, on further investigation, the results here attained to shall be confirmed, should of themselves be regarded as at least of equal value with such eminently variable characters as the number of pores or the distribution of miliary tubercles. But, while I thus exhibit a somewhat stronger inclination than Prof. Agassiz to keep the species separate, I shall, no less than he, look out anxiously for those intermediate forms, of which he speaks with such confidence. i ii iii v Absolute diameter in millims. 17 19-2 31 33-5 41 Height. 84-7 87-5 91-9 92-8 103 Percentag Abactinal area. 15-2 15-6 19-3 19-4 146 e value of Anal area. 10-3 9*8 Actinostome. 323 31-8 30-6 32-8 22-6 Poriferous zone. 11 1-2 1-9 2 2 VI. HOLOPNEUSTES. HOLOPNEUSTES POROSISSIMUS. The single specimen by which this genus or subgenus is represented in the Museum belongs, I fancy, to this species, and not to H. purpurascens, as stated by Prof. Agassiz. I give the more important measurements, which throw into relief the rather small size of the actinal and abactinal areas, and the extraordinary development of the poriferous zone. Percentage value of Diameter. Abactinal Poriferous millims Height. area. Anal area, Actinostome. zone. 52 78*8 15*3 6*9 22*1 6*2 1 Zoophytes, pl. ii. |