98 GEOLOGICAL RECONNAISSANCE OF THE DOM NICAN REPUBLIC. 



formation but not in the typical Cercado formation — Conus consobrinus 

 Sowerby, Conus marginatus Sowerby, Fasciolaria semistriata Sowerby, and 

 Metulella venusta (Sowerby). 



Gurabo Formation. 



The faunal lists for the Gurabo formation are incomplete, as the Forami- 

 nifera obtained in it have not been identified; the fauna here recorded 

 consists mostly of corals and mollusks. One of the striking peculiarities of 

 the formation is the relatively rich coral fauna, comprising between 70 and 

 80 species, a considerable number of which, particularly in its upper part, 

 are of reef facies. Although several species also occur in the underlying 

 Cercado formation and others range upward into the overlying Mao Aden- 

 tro limestone, the assemblage differs from that of each of the adjacent for- 

 mations and some species appear to be confined to it, for example, Aster o- 

 smilia abnormalis (Duncan), A. exarata Duncan, A. profunda (Duncan), 

 A. hilli Vaughan, Teleiophyllia grandis Duncan, and Syzygophyllia dentata 

 (Duncan). Several of the species occur in the Cercado formation and in 

 the lower part of the Gurabo; others occur in the upper part of the Gurabo 

 and in the Mao Adentro limestone. It is therefore possible to tell the part 

 of the formation from which a fairly large collection of well-preserved 

 corals came. 



About 400 species of Mollusca have been recognized in the Gurabo forma- 

 tion, and almost half of these species are not known in the typical Cercado 

 formation. The most abundant species that do not occur in the typical 

 Cercado formation are Terebra sulcifera Sowerby, Conus haytensis Sowerby, 

 Conus symmetricus Sowerby and subsp. domingensis Sowerby, "Clavatula" 

 labiata Gabb, "Drillia" venusta (Sowerby), Lyria pulchella (Sowerby), 

 Murex domingensis Sowerby, Metidella venusta (Sowerby), Distortio 

 simillima (Sowerby), Sconsia laevigata (Sowerby), Morum domingense 

 (Sowerby), Crepaticella capula Guppy, Pecten (Aequipecten) eugrammatus 

 Dall, Echinochama antiquata Maury not Dall, and Cytherea (Ventricola) 

 blandiana (Guppy). The largest shoal- water faunules were collected on 

 Rio Mao at stations 8519 (Maury's Bluff 1) and 8734, and on Rio Amina 

 (station 8516). The large collection from Rio Yaque del Norte (station 

 8702) includes several groups, such as Leucosyrinx, Pleurotomella, Caricella, 

 and Verticordia (Trigonulina) , that indicate deeper water. Several species 

 of Mollusca are confined to certain horizons within the Gurabo formation, 

 so that subdivisions of the formation can be recognized. 



The Bowden marl of Jamaica is apparently of about the same age as the 

 Gurabo formation. Woodring has recently completed a monograph on the 

 Mollusca of the Bowden marl, which has been submitted to the Carnegie 

 Institution of Washington for publication. 1 The Bowden molluscan 



1 Vaughan, T. W., Carnegie Institution of Washington Year Book No. 18, p. 345, 1920. 



