44 Dr. T. Wright on new Species of Echinodermata 



extend into the mouth ; this opening is in the centre of the disc, 

 and has a subpcntagonal form ; it is of a moderate size, and is 

 surrounded by ten stout spines formed by the development of 

 the first lateral plates, which are much expanded and terminate 

 at the oral border in short stout spinous processes ; the lateral 

 plates from the adjoining rays are here united together, so that 

 two spines from the lateral plates of different rays are closely 

 approximated, and the five rays are thereby united together 

 round the mouth-opening like five Gothic arches, so that the 

 mouth with its channels, formed by these arches, resembles a 

 miniature starfish in the centre of the disc; the five pairs of 

 spines may have served as jaws. 



Affinities and differences. Our knowledge of fossil Ophiuridce 

 is unfortunately so limited, and the details of those forms 

 known are so meagre, that there is much difficulty in making 

 a comparison between the extinct genera of this family. In our 

 description of Ophioderma Gaveyi a diagnosis has been attempted 

 between it and O. Milleri, Phil., both of these being Liasic spe- 

 cies. The other forms hitherto published are those figured by 

 Goldfuss, namely the Ophiura prisca, Miinster, from the Muschel- 

 kalkof Baireuth; the Ophiura loricata, Goldf., from the Muschel- 

 kalk of Wiirtemberg ; the Ophiura speciosa and O. carinata, 

 Miinster, from the Lithographic slates of Solenhofen ; of these 

 Goldfuss's figures are excellent, and leave nothing to be desired, 

 as that able natural-history artist Herr Hohe, whose crayon has 

 added such lasting value to the ' Petrefacta Germanic/ has given 

 accurate details of structure which prevent the possibility of con- 

 fusion regarding the identification of the species drawn by him. 



The Ophiura Egertoni, Brod. *, found in nodules of micaceous 

 sandstone at the base of the Inferior Oolite near Charmouth, is 

 so entirely distinct from our fossil, that to mistake them is im- 

 possible ; between O. Griesbachii and O. speciosa and O. carinata, 

 the difference is likewise very great ; O. loricata comes nearer to 

 our Brittle -star than either of the others, but the great develop- 

 ment of the lateral plates of the rays, and the clasping and im- 

 bricated character of the same in O. Griesbachii, forms a struc- 

 tural character which separates it widely from Goldf uss's species. 

 If we seek further for resemblances to our Brittle-star, we must 

 look for them more amongst the beautiful Ophiocoma of our 

 seas than among any forms we are acquainted with in the fossil 

 state, but even between it and them the differences are many and 

 distinct. 



Locality and stratigraphical range. This beautiful fossil was 

 collected by the Rev. A. W. Griesbach from the Forest marble of 



* Geol. Trans. 2nd series, vol. v. pi. 12. 



