66 Mr. J. Thomson and Dr. H. A. Nicholson on the 



sidering Cyathopsis a synonym of Amplexus^ as insisted on by 

 Edwards and Haime. The same authorities can equally be 

 followed in referring most of the species of Caninia to the genus 

 ZapJirentis. 



There is, however, one species of Caninia, viz. the Caninia 

 gigantea of Michelin, which, in our opinion, cannot possibly 

 be referred to Zaphrentis without violating its natural affini- 

 ties. This species was removed from Caninia to Zaplirentis 

 by MilnC'Edwards and Haime ; and its name was at the same 

 time changed to Z, cylindrica, in consequence of there being 

 already in existence the much older Z. gigantea of Lesueur, 

 which is an unquestionable Zaphrentis, We are, however, 

 satisfied that the coral known under the names of G. gigantea, 

 Mich., or Z, cylindrica, E. & H., possesses a structure which 

 removes it out of Zaphrentis proper, as will at once be evident 

 from the following brief summary of its leading characters : — • 



Corallum (PL VI. figs. 1^1 1) tall, cylindrical or cylindro- 

 conical, more or less curved, with distinct accretion-swellings. 

 Epitheca thin, with fine encircling lines of growth. Calice 

 circular and shallow. The central area of the coral is occupied 

 exclusively by the tabulee, which are close-set and numerous, 

 and bend down slightly at the margins of the area. Circum- 

 ferentially there is a large, distinct, and well-developed zone of 

 vesicular tissue, formed by dissepiments filling the interaeptal 

 loculi, and constituting a series of minute lenticular cells ar- 

 ranged in rows which have a direction upwards and outwards. 

 The septa are well developed, but do not appear to extend to 

 the centre of the visceral chamber, a portion of the central 

 tabulate area being left exposed to view. The primary septa 

 are numerous, apparently always over sixty in number towards 

 the summit of the corallum, and they alternate with much 

 shorter secondary septa. A single well-marked septal fossette 

 is present, placed on one side, formed by a depression of the 

 tabulse, and occupied by a single short septum. 



D'Orbigny selected as the type of the genus, viz. Cyathopsis {AmplexHs) 

 cornu-bovis, Mich. This coral diiFers from typical species of the older 

 genus Ainplextis (such as A. coralloides, Sow.) chiefly in the fact that the 

 septa extend fm-ther inwards towards the centre of the visceral chamber. 

 The distinction relied upon by D"Orbigny is that A. cornu-hovis possesses 

 a septal fossette formed by an inflection of the tabidas on one side ; but a 

 similar, though less pronounced, fossette is present in A. coralloides ; so 

 that this distinction falls to the ground. The development of the septa in 

 A. coniu-bovis, though greater than in A. coralloides, is not suflicient to 

 constitute a groimd of generic distinction, since in both forms a large 

 central area of the tabulae is left exposed to view. We have not seen the 

 original specimens of A. cormi-bovis, Mich. ; but we figure an example, 

 apparently belonging to this species (PL VII. figs. 6, 6 a), which shows 

 the characters of the septa, and can be compared with the figures we have 

 previously given of Amplexus, 



