REPORT ON THE ALCYONARIA. 45 



developed. This genus stands very near to Mopsea; the spicules closely resemble those 

 of Mopsea dichotoma, but, apart from the different habit of the colony, the polyps show 

 a totally different form, and most of the branches arise from the middle of the calcareous 

 joints. 



As yet only one species can with certainty be referred to this genus. Perhaps also 

 the Mopsea costata from the London clay, cited by Milne-Edwards and Haime,* belongs 

 to it. 



Acanthoisis Jlabellum, n. sp. (PI. VIII. figs. 1, la, l6 ; PI. IX. fig. 12). 



The colony is expanded like a fan, and plumosely branched. The main stem gives 

 off larger branches and smaller twigs alternately on two sides, which come off nearly at 

 right angles. The small twigs generally remain simple, the larger branches bend round 

 after a short course and run parallel to, or at sharp angles with the main stem, themselves 

 again branching further just like the latter, bearing partly larger twigs, which again give 

 off lateral twigs, and partly small unbranched twigs that stand out at right angles. Twigs 

 of the fifth order may thus be developed. Only in individual places do two branches 

 anastomose with one another, most of them are free. Superficially regarded, we have a 

 number of radiating branches diverging in one plane, which are provided with two rows 

 of twigs like a feather. The main stem has a diameter of 1"5 mm. at the base and a 

 length of 95 mm., the larger branches attain a length of 80 to 90 mm., the smaller 

 branches 5 to 10 mm. The entire height of the colony reaches 110 mm., the greatest 

 breadth 100 mm. 



The polyps are placed on the stem and branches in short spirals, four or five in a 

 spiral ; only on the thin, somewhat flattened, terminal twigs are the polyps placed on 

 both sides of the axis. A short process of the ccenenchyma forms the end of each twig. 

 The polyps are shaped like truncated cones. They arise with broad bases and diminish 

 slightly in size towards the mouth, which appears to be evenly truncated, since the 

 tentacles are folded in at right angles over the oral cavity. The polyps stand up 

 straight from their axis ; only on the point of the twig are they placed obliquely to the 

 stem. Their height reaches 0'4 mm. and the diameter at the base 0'5 mm. 



The axis consists of alternating joints of thick calcareous substance and intervening 

 masses of horn. In the thicker parts of the stem the calcareous joints are twice as long 

 as the horny joints, 3 mm. ; in the branches and especially in the terminal twigs they 

 become considerably longer than the horny joints, which have a much smaller diameter 

 than the calcareous joints. The latter have a spindle-like form. The last joint is always 

 calcareous. In the stem the calcareous joints are whitish, in the twigs they assume a 

 reddish-yellow colour. The branches arise from each calcareous joint to the number of 

 two, at different heights, from each side. Sometimes the first horny joint of the higher 



* Monogr. British Fossil Corals, p. 42, pi. vii. fig. 3. 



