108 PROCEEDINGS OP THE 



the same time, it shews the difficulty that exists, and the great 

 care that is required in coming to correct conclusions regarding the 

 true nature of these lowly forms. 



The Chairman exhibited specimens of a new species of Archaeo- 

 cidaris, a fossil sea urchin, and a species of Siliquaria, a tubular 

 univalve shell, both forms being from the collection of Dr. Rankin, 

 Carluke, which was recently presented by him to the Hunterian 

 Museum. The new species of Archaeocidaris is only known as yet 

 by its larger spines, which bear four rows of smaller spines or 

 denticles, their peculiarity being that they are long and thorn-like, 

 and stand out from the body of the main spine at nearly right 

 angles, whereas the denticles on the other species of Archaeocidaris 

 are shorter, and clasp or point to the upper end of the spines at 

 acute angles. Specimens of this species have been submitted to 

 Dr. Wright, of Cheltenham, an authority on fossil sea urchins, and 

 he is likewise satisfied that it is still an undescribed one. 

 It has only as yet been found in the limestone shales at Gillfoot, 

 Carluke, and the Chairman (Mr. Young) has provisionally named 

 it after its discoverer Archaeocidaris Ranlrinii. The other fossils 

 from Dr. Rankin's collection were referred, rather doubtfully, to 

 Siliquaria, a genus which has not hitherto been identified from 

 older strata than the Eocene beds of the Tertiary formation, and 

 which is only represented at present by seven living species, found 

 chiefly in sponges. The specimens, which are three in number, 

 may be considered unique, and were found in the shales of the 

 Gare limestone series at Carluke. They consist of fragments of 

 tube-like whorls of a large spiral shell, the tubes being nearly one- 

 half inch in diameter, and shewing a moderately thick shell. After 

 a careful examination of these fragments Mr. Young could only 

 refer them to the genus Siliquaria, which is characterised by having 

 an open tubular shell with a continuous open narrow slit running 

 along the whole length of the tube. The Carboniferous species 

 seem to agree with the recent shells in this respect, and they 

 further agree in having the slit along the upper and outer sides of 

 the whorls of the tubes, the shell growth being likewise seen to 

 run parallel with the edges of the slit, shewing that it could not be 

 due to accidental fracture. Should the identification of these 

 specimens with Siliquaria be confirmed by the discovery of other 

 specimens, Mr. Young proposed to name this species S. carbonaria, 

 to denote the formation from which they were obtained. 



