Mr. H. Seeley on a new Order of Echinoderms. 365 



XLIII. — Notes on Cambridge Palaontology. 

 By Harry Seeley. 



, III. On a new Order of Echinodenns. 



Introduction. — For many years past there have been observed 

 in the Upper Grcensand, near Cambridge, certain forms of an 

 anomalous organism which it seemed impossible to gronp in an)'' 

 known family or order of Invertebrata. As yet, no opinion has 

 been expressed on their affinities; and as these are by no means 

 evident at a glance, it has been thought desirable to give a sketch 

 of the evidence which has led to the conclusions to be presently 

 stated. 



The bodies in question consist of carbonate of lime with a very 

 slight animal basis ; so that without much difficulty the cleavage- 

 faces may be obtained. The form of the larger and more com- 

 mon type is an elongated sphere, with a longitudinal wedge- 

 shaped slit, the margins of which are tuberculated ; it is granu- 

 lated, and has one end flattened and smooth. From these cha- 

 racters it is evident that the structure is Echinodermatous, 

 though to what group of Echinoderms it belongs is far from 

 clear. 



Its shape and the tubercles would at first sight suggest its 

 place to be in the Echinoidea ; but the cause of the failure of 

 our efforts to find apertures, or ambulacra, is soon explained by 

 discovering it to be solid. Nor is there any probability of its 

 being an Urchin-spine, since, besides the fact of its being chan- 

 nelled, the tuberculated character would be altogether unique. 

 It clearly has nothing to do with the Echinoidea. 



The slit and general form give it a resemblance to the joints 

 of the arms of a Crinoid ; but besides the fact that no Crinoid 

 has yet been observed with the margui of the groove tubercu- 

 lated, there is the more important one that it has but one end 

 fitted for articidation, the other being convex and granulated. 

 Among the Ophiuroidca there is no structure with which it has 

 the slightest analogy. So we are reduced to placing it among 

 the Star-fishes. But here, too, the same structural difficulties 

 are met with. The single attachment at once excludes it from 

 being a part of the skeleton of either that group of Star-fishes 

 in which it consists of a network of membrane with the meshes 

 of bone, or of that iu which there is a network of bone with the 

 meshes of membrane. To this, however, there is an exception^ 

 since in some species of Goniodiscus there is developed, at the 

 extremity of each corner, a single plate, under which the eye is 

 lodged. This plate, though attached to the two great oculars, 

 has itself but a single articulation. In proportions it resembles 



