It. F. Tomes — British CreUiceous Madreporaria. 



299 



the genus. It was created in 1851 by MM. Milne Edwards and 

 Haime ' for the reception of a single British species from the Green- 

 sand of Blackdown, Simloirnchus tiiherosvs, which tliey had ah'eady 

 plaeed, though with doubt, in the genus Troclwsmilia.'^ Afterwards, 

 that is to say in 1857," they brought two other species into the genus, 

 one of them from the Farringdon Greensand, Smilotrochus Austeni, 

 and the otlier, S. Hagenowi, from the White Chalk of Maestricht. 



The " Introduction " of Dr. de Fromentel, which appeared in 

 1858-61. made no addition to or alteration of either genus or species ; 

 but in 1869 and 1870* Professor Duncan, while including the two 

 British species above mentioned, added five others to the genus, 

 making in all seven British species. In 1885 the present writer* 

 described and figured an eighth ; but both it and all those added by 

 Professor Duncan have now beeTi found to appertain to other genera. 

 Moreover, Smilotrochus tnberoms, the ver^' si)ecies on which the genus 

 was founded, is in the present communication shown to be a Placo- 

 smilia. As a genus, therefore, Sinilotrochus now rests on two 

 species, S. AiiHfeni and S. Ilaijenowi. Of the former so little is 

 known that a re-examination is most desirable, and all the more so 

 as so many simple Cretaceous corals have proved on close examination 

 to appei'tain to genera characterized by the presence of a columella 

 or pali, or of both. 



Before entering into the details of the several species, I wish to 

 record my indebtedness to Dr. Blackmore, of Salisbury, by whose 

 kindness I have recently examined a collection of corals from the 

 Chalk of that neiglibonrhood, some of which will shortly be mentioned. 

 He has also favoured me with a section of the Salisbury Chalk, which 

 enables me to place the several species in their precise position in the 

 formation, and also to give theii* relative frequency, as follows: — 



1. Zoue of BclemnitcUa mucrouafa, 

 the highest beds, corresponding 

 to the beds of NorfoJk and 

 Dorchester. 



2. Zone of Acthwcamax quadrata, 

 chiefly exposed at East and 

 West Haruham, and worked 

 for whitening. 



3. Zone oi 2Iarsitpltcs 



4. Zone of Micraster cor-anguinum 



Feet, r 0. 

 80 4 P, 



Onchotrochus scrpentmus. 



'mlosmilia laxa. 

 Farasmilia eentrulis. 

 Mantelli. 



170 



230 



250 



Axogaster cretacea. 

 Farasmilia centralis. 



3Ia)itelli. 



• • Gravensis. 



C'oelosmilia laxa. 



rec/ularis. 



Diblasas Gravensis. 

 Stepkanophijllia mcmismalis. 

 Axogaster cretacea. 

 Garyophgllia cglinclracea. 

 Parasmiiia centralis. 

 Axogaster cretacea. 

 Caryophyllia cylindracea. 

 Parasinilia centralis. 

 serpentina. 



1 Pol. Foss. Terr. Paleoz., 1851, p. 29. 



2 Brit. Fos. Cor., 1851, p. 58, pi. x, fig. 2. 

 ■* Hist. Nat. Cor., t. ii (1857), p. 71. 



* Supp. Brit. Fos. Cor., pt. ii, Xo. 1, p. 19 , and pt. ii, No. 2, p. 36 (1869-70). 

 ^ Geol. Mag., December, 1885. 



