59 



1 . Ambulacris angustioribus : poris mediocribus approximatis. 



a. Ore subintegro. 



Of this section Ech. esculentus may be regarded as the type. 



On this species Mr. Gray incidMitaUy remarked that it is extremely 

 variable in shape, becoming very high and subconical in the adult age, 

 when it is Ech. Melo, Lam. ; and being often subangular, in which 

 condition it is Ech. subangulosus, Ejusd, 



b. Ore profunde iaciso. 



Ech. excavatus, Lam. ; Ech. Pileolus, Lam. ; &c. 



2. Ambulacris latis : poris inter se tuberculis parvis sejunctis : 

 ore 5-inciso. 



Ech. ventricosus, Lam. ; &c. 



Genus 4. Echinom'etra. 



Corpus plūs minusve depressum, saepė oblongum. 



Area ambulacrorum mediocres : tesserce ambulacrales quinquariam 



vel ultra biporosse. 

 TessercB ovariales et interovariales mediocres. 

 Anus subcentraUs, sąuamosus ; squamis saepe spiniferis. 



In this genus the ambulacral platės may be considered as being 

 composed of five or more doubly pierced pieces, which form an 

 arched line round the outer edge of the tessera, -vvith a single pair 

 of pores at its lower inner angle. 



TTie spines with which the species of this genus are fumished are 

 often of very unequal size, and they are of very variable form, some 

 of the larger ones being very long, as in Echinometra trigonaria ; 

 and others very short and truncated, as in Ech. atrata. 



Mr. Gray ste.ted that he had formerly separated from the Echini 

 some of the species of this genus which are peculiar for their oblong 

 form, and that the genus so proposed by him had been adopted by 

 M. de Blainville ; but a much more extended examination has con- 

 vinced him that individuals of the šame species vary from roundish to 

 oblong : and, therefore, having observed many round species agree- 

 ing with oblong ones in the peculiar character of the ambulacra, he 

 has united them to the former, under the šame name. It is to be 

 remarked, as throwing doubt on the bilaterality of the EchinidtB, 

 attempted to be established by M. Agassiz, that the spongy ovarial 

 plate which that gentleman regarded as the mark of the hinder part 

 of the Echinida, is alvrays placed on one side or the other of the 

 longer axis of the oblong species. 



This genus vdll contain sections B**. D. and F. of M. de Blain- 

 ville, as well as the Echinometra of that author, and many new spe- 

 cies which are as yet undescribed. 



Mr. Gray sub8equently exhibited a specimen of a new genus of 

 Corals, which he had recently received from the coast of Montserrat 

 in the West Indies. The coral in question is formed almost entirely 

 of rather large transparent rough fusiform spicula, which are irre- 



