IDMONEID^E. 95 



anastomosing rarnuscules. In the latter case the growth bears a strong resemblance to 

 that of a Retepore, with which genus consequently the Horncree, or many of them, were 

 formerly associated by Lamarck and others. 



Of the genus as thus restricted, five or six recent species exist, divisible like the fossil 

 into the "ramose" and " fenestrate." Three belonging to the former, and two or three 

 to the latter. 



The three ramose living Horneras with which I am acquainted are : 



1. H. FB.ONDICULATA, Lamouroux. 



2. H. BOREALIS (mihi, MS.) 



3. H. TRIDACTYLITES (mihi, MS.) 



The first is the well-known Mediterranean form, originally figured by Ellis, subse- 

 quently named Hornera frondiculata by Lamouroux, and which has since been figured and 

 described by Milne Edwards (' Mem. s. les Crisies/ &c., 1. c.). 



The second, is a species collected by Mr. M'Andrew on the Coast of Norway and 

 Finmark, and by Captain Beaufort in lat. 61 35' N., 90 42' W., and which is not 

 improbably the same as that mentioned by Lamouroux as occurring in Karntschatka. 

 This I formerly described and figured in the 'Ann. Nat. Hist.,' 2d ser. 18, p. 34, pi. i, 

 fig. 7, under the erroneous appellation of H. frondiculata, from which subsequent investi- 

 gation has shown it to be wholly distinct. 



Of the third species I have specimens collected by Mr. Darwin on the shores of 

 Patagonia and Tierra del Euego, and by Mr. M'Gillivray in the Australian seas, but no 

 description or figures of it have as yet been published. It probably represents the form 

 noticed by Lamouroux as found in the Indian and Australian seas. It differs in all 

 respects from the other two. 



Of the fenestrate kind I am acquainted with two forms, apparently distinct species, 

 both of which I believe to be, and one certainly is, Australian. No account of this species, 

 of which very perfect specimens were brought by Mr. Gould from South Australia, has 

 yet been published, although figures of it have been prepared. I propose to call it 

 Hornera gouldiana. 



Several fossil forms of Hornera have been noticed, and some of them figured ; but 

 from the want of precision in the details of the figures, and the absence of any determi- 

 nate specific characters in the descriptions, it is extremely difficult to arrive at any satis- 

 factory conclusions with respect to them. The best figures are those contained in Milne 

 Edwards's excellent ' Memoir on the Crisise/ &c. ; but even these are by no means suffi- 

 ciently precise to convey a correct idea of the specific differences or resemblances. 



I have, therefore, had the utmost difficulty in coming to any conclusion satisfactory to 

 myself with respect to the fossil species of Horncra contained in the Crag, and I would 

 hardly venture even now, after the most laborious endeavours to ascertain the truth, to 



