THE ANNALS 



MAGAZINE OF NATURAL HISTORY. 



[THIRD SERIES.] 

 No. 72. DECEMBER 1863. 



XLI. — On Polytrema miniaceum, a Polythalamian. 

 By Professor Max Schultze*. 

 [Plate VII. figs. 1-10.] 

 Under the name of Polytrema corallina, Rissof describes cer- 

 tain small, red, coral-like calcareous structures which occur 

 pretty widely in the Mediterranean upon seaweeds, shells, and 

 other marine productions. They form calcareous crusts, mea- 

 suring 3-4 millims. or less in their greatest diameter, of a dingy 

 carmine-red colour, and with an irregular surface ; they adhere 

 firmly usually to a flat surface, but are also frequently met with 

 forming rings round thin stems of Algae. 



These structures resemble small Millepores, with which in- 

 deed they were formerly placed. Linnsus's Millepora miniacea J 

 must be referred to our species. Lamarck describes them as 

 Millepora rubra ^, whilst DeBlainville|| combined Bisso's generic 

 name Polytrema with the Linnsean specific name miniacea (or, 

 more properly, miniaceum), which appellation is here adopted. 



On the surface of these structures the lens shows numerous 

 roundish shallow depressions, which extend equally over the 

 lobed or cock'scomb-like elevations and over the depressed 

 parts between these. (PI. VII. fig. 1). The depressions are 

 usually very shallow, and are occupied at the bottom by pre- 

 cisely the same mass which is seen between them. Frequently 

 the bottom of the little depressions rises in the form of a some- 

 what spherical dome, like a mountain cone ascending from the 

 depths of a crater and gradually filling the latter completely. 



* Translated by W. S. Dallas, F.L.S., from Wiegmann's Ai-chiv, 1863, 

 p. 81. 



t Hist. Nat. Eur. Merid. v. p. 340, 



X Systema Naturae, ed. Gmel. vi. p. 3784. 



§ Hist. Nat. Aiiim. sans Vert. || Man. d'Actiu. p. 410, ])1. 69. fig. 4. 



Ann. ^ Mag. N. Hist. Ser. 3. Vol. xii. 27 



