INTRODUCTION. 



iii 



structure that the closest scrutiny only detects the slightest specific modification between 

 the Urasters of the Lias and those from our shores. 



The Tropidasterid/E, Wright, have a stellate body with short rays and variable as 

 to numbers. The upper surface is covered with solitary or fasciculated spines, 

 arranged in regular order. The ambulacral areas are bordered by fasciculi of spines 

 disposed in rows more or less numerous. There are two rows of pores for the passage 

 of the tubular feet, by which they are distinguished from the Urasterid^, in which they 

 are quadriserial. The vent is dorsal and excentral in the Solasters. This family ranges 

 from the Lias seas to those of our day. The Tropidasters lived in the Lias period, and 

 the Solasters have lived on from the Lower Jurassic times into the present time. 



The AsTEROiDEA are very well represented by eight genera, and twenty-three species 

 in English Jurassic strata, and the anatomy of these skeletons has been fairly made out 

 in these native fossil forms. 



The Ophuroidea are grouped into two families, the OpHiURiDiE and Asterophidi^. 



The OpHiURiDiE contain five genera that have representatives in our Jurassic strata. 

 The structure of the body-disk in this family is so delicate and fragile, and consequently 

 more or less injured or utterly destroyed in the fossil state, that its structure is made out 

 with great difficulty, and often with much uncertainty. Should better specimens be 

 discovered hereafter with their anatomical characters better preserved, then our errors, if 

 any, can be corrected. With the materials at my disposal I have been scrupulously 

 careful, with the aid of the lens and the microscope, to submit all these parts to a most 

 minute inspection ; still we cannot revive traces of organic structure when they are 

 hopelessly effaced, therefore some of ray diagnoses of genera and species are neither as 

 complete or precise as I should have wished them to be from causes which I was unable 

 to control. 



My most kind and considerate friend, our worthy secretary, the Rev. Thos. Wiltshire, 

 F.G.S., knowing how much my time is occupied with public duties, has generously 

 prepared a summary and analysis of the families and genera of the Echinoidea, 

 AsTEROiDEA, and Ophiuroidea, described in the two volumes of the ' Oolitic Echino- 

 dermata.' This important addition to my work will be very useful to students, as it 



