792 W. J. BOLLA.S OX THE STRUCTURE AND 



1770. Guettard. 'Mora, sur les Sci. et Arts,' torn. ii. p. 100, " l)e 

 la structure des Polypites ou Polypiers fossiles ;" p. 317, " Ar- 

 rangement niethodique des Polypites." 



In these papers a very full and accurate description, illustrated 

 with numerous figures, is given of various Siphonice. They consti- 

 tute as " Caricoi'des " the first genus of the class of polypites, which 

 are defined as " marine fossil bodies of various forms, branched or 

 not, pierced by simple or stellate holes, and which in their original 

 state were formed by polyps contained in these holes." 



After a definition of the genus very similar to that of 1751, a 

 number of species are described and figured, including among them 

 a " Caricoi'de with five or six ribs," which is a veritable Siplionia 

 costata (Hallirhoa, Lamx.). 



Altogether, in Guettard's hands, the Caricoi'des form a very natural 

 group. 



1778. Schroter. ; Vollstandige Einleitung in d. Kenntniss u. Ge- 

 schichte d. Steine u. Versteinerungen,' vol. iii. p. 431. 



To this work I have unfortunately not succeeded in obtaining 

 access. 



1808. Parkinson. ' Organic Remains of a Former World,' vol. ii. 

 p. 95, plate ix. figs. 4, 7, 8, 11, 12, 13, plate xi. fig. 8. 



Parkinson considers that we must in most cases give up every idea 

 of distinguishing between Alcyonia and sponges in the fossil state. 

 He refers Guettard's forms to one or the other without deciding 

 which, and at the same time regards some of them, e. g. that 

 figured by him on plate ix. fig. 4, as presenting, along with cha- 

 racteristic differences, a very striking resemblance to Alcyonium ficus, 

 Linn. 



Parkinson's contributions to our knowledge of the genus consist 

 chiefly of quotations from Guettard, and of figures of sections taken 

 longitudinally and transversely through the sponge (plate ix. figs. 

 7, 12, 13). 



1814. T. Webster. ' Geological Transactions,' ser. 1, vol. iii. 

 p. 378, pis. 27-30. 



In a letter to Sir Henry Englefield, dated Aug. 21, 1811, this 

 author describes some silicified remains of sponges, one form of 

 which he names Ci tulip-alcyonium." This consists of a head, com- 

 posed of a group of more or less parallel tubules, without a central 

 cloaca at the summit, and supported below on a slender stem some 

 four or five feet in length ; it occurs abundantly in the Greensand 

 of Western Lines, Isle of Wight. 



This form appears to be a true Siplionia, though it possesses no 

 central cloaca, and as a consequence its excurrent canals are arranged 

 in a longitudinal fascia, and open on a plane area at the summit — 

 an arrangement which is usually regarded as diagnostic of Jerea. 



