of Hippotlioa and Alecto. 125 



James, from which it is distinguished mainly by its more 

 slender habit and graceful form, and by its generally having 

 its cells arranged in a double or single series. Also, I have 

 not hitherto been al)le to make out in the texture of yl. aulo- 

 poroi'de^ the minute pores which seem to be present in all 

 perfect examj)les of A. frondosa. 



Locality and Formation. — Cincinnati Group, Cinciiuiati, 

 Ohio. The species is a common one, and is found upon 

 Strophomena alternata, Conrad, and Streptelasina comiculnm. 

 Hall. ' 



3. Alecto Jrondosa, James. PL XI. figs. 3-3 d. 



Atilopora frondosa, James. Named, but not fip^ured or described, in 

 tlie 'Catalogue of the Lower Silurian Fossils of the Cincinnati 

 Group,' 1871, 



Polyzoar}^ creeping, adnate, of reticulating and anastomosing 

 branches, Avhich usually become more or less completely eon- 

 fluent so as to give rise to a thin expanded crust, or which are 

 partially reticulated and partially confluent. When the branches 

 form a network, the size of the meshes, as well as their disposi- 

 tion, is exceedingly variable ; but they are usually more or 

 less oval, with a long diameter of half a line to a line or more, 

 the interspaces between them varying from half a line to two 

 lines. The cells are uniscrial on the narrowest branches, but 

 biserial, triscrial, or multiserial on other parts of the coenoecium ; 

 elongated and tubular, immersed below, but free towards their 

 apertures, the terminal portion of the tube being more or less 

 elevated above the general surface. Cells from six to eight 

 in the space of one line. Cell-mouths terminal, circular, of 

 the same diameter as the tube. Entire surface, in well pre- 

 served specimens, minutely porous. 



There does not appear to be any reason for doubting that 

 this is a true Alecto. It is nearly allied to A. auloporoides, 

 especially as regards the form of the cells ,• but the greater 

 width of the branches and their common coalescence into ex- 

 panded crusts, together with the greater number of the rows 

 of cells over most portions of the coenoecium, communicate to 

 the fossil quite a peculiar appearance, and appear to be cha- 

 racters of specific value. Since my original description of 

 this species, founded on type specimens furnished me by Mr. 

 James, was written (in the Report on the Fossil Corals, 

 Polyzoa, and Sponges of the State of Ohio, now in course 

 of publication), I have examined a large suite of specimens 

 which I collected myself at Cincinnati. These enable me to 

 assert that, in all well-preserved examples, the entire surface of 

 the polyzoary is covered with the apertures of exceedingly 



