PORIFERA. II. 187 



dermal spicules. Osc?da scattered. The skeleton an irregular reticulation of spiculn-bii /idles and single 

 spicules. Spicula: Mcgasclcra : the skeletal spicules oxca 0-56 — 0-68"""; the dermal spicules tylota o-j2 

 — 0-42"""; microsclera of t7VO forms, isancorcc nnguiferce with nine to thirteen free teeth 0-048 — 0-065""" . 

 birohilee with thirteen to ca. twenty teeth 0-015 — 0-020""". 



This species is of a quite irregular, most frequently tuberous or lumpy form; one specimen is 

 more regularly roundish. Sometimes it forms thick incrustations, and one individual, presumably a 

 very young one, forms a small, thin incrustation. The typical form evidently is from a tolerably thick 

 incrustation to a more or less irregular lump. The largest specimen has a greatest extent of fully 

 40™, but I think it may grow larger, as we have specimens of similar sizes, which are not entire 

 ones. It grows on shells of mollusca, on other sponges, and frequently on loose bottom material, as 

 small shells or pebbles and gravel. The colour (in spirit) is a dirt}- brown of a lighter or darker 

 shade. The consistency, as it seems, ma)' be a little varying, from middle firm to somewhat firmer, 

 most frequently, however, it is rather brittle. The surface, where it is undamaged, seems to be about 

 smooth, or at most slightly shaggy. The dermal -membrane is a thin, transparent film, which, when 

 detached, has a tendency to contract. It is supported by bundles of dermal spicules. Pores were only 

 seen here and there on the surface, gathered into pore-sieves, in which the single pores are only 

 separated by thin strings of tissue. Their size was measured to 0-07 — o - 24" ,m . Oscula are found scat- 

 tered as circular apertures, sometimes the dermal membrane rises a little round them like a spout. 



The skeleton. The dermal skeleton consists of more or less penicillate bundles of dermal spicules, 

 which may be erect or more or less recumbent. The dermal skeleton is often very little developed, 

 the bundles being placed with great intervals, and then the membrane seems to be resting on the 

 skeleton below, the spicules of which may project; this feature, however, is perhaps due to contraction, 

 but as the dermal membrane is highly damaged in all the specimens in hand, it cannot be decided 

 with certainty. The main skeleton is an irregular reticulation of spicula-bundles and partly single 

 spicules, forming quite irregular meshes. Fibres are not formed. The sponge is most frequently rather 

 lacunous, on account of the man}- canals, chiefly running towards the surface. Spongin is found where 

 the spicula join in the skeleton, but only to a rather slight amount. The sponge frequently embodies 

 foreign bodies copiously, as foramiuifera, gravel and the like. 



Spicula: a. Mcgasclcra. 1. The skeletal spicules are oxea, they are slightly curved, some- 

 times with a somewhat sharper bend in the middle, and then the}- show some resemblance to the oxea 

 in H. panicca. They taper only very little from the middle outward, the point itself is middle long. 

 Their length is 0-56 — o - 68 mm , and the thickness in the middle is 0-014 — o-020 mm . Developmental forms, 

 down to quite fine ones, occurred in small numbers. 2. The dermal spicules are tylota with toler- 

 ably well developed end-swellings; the}- are most frequently straight; sometimes they may be quite 

 slightly curved; the}- are about cylindrical. Their length varies from 032 — 0-42"™, in a few cases the} 

 ma}- be still a little longer, but most frequently the length is about midway between the two sizes 

 given, ca. o - 37 mm . The thickness is o - oo6 — o - oo85 mm . In the fully developed tylota no difference or 

 only a slight one is found between the two ends, but such a difference is found in the developmental 

 forms; the finer they are, the thinner is one end, and its swelling is more longish than that of the 



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