338 GENERAL SUMMARY TO 



Many of the species of Discina and Discinisca (Dall) live clustered together in vast 

 numbers, and adhering, in all their stages of growth, by their peduncle to the surface of 

 the shell of their neighbour, one above the other, till they form a living mass of con- 

 siderable breadth and thickness. Thousands of Discinisca Icevis or lamellosa were 

 obtained by Mr. F. H. Brady at Callas, Peru, and a number of them in this condition 

 were sent to me in 1872 by Prof. Verrill. Rocks in which Lingula and Discina are found 

 would therefore indicate seas of very moderate depth, for we have no reason to suppose 

 that the same kind of animal, in times long past, differed materially in its mode of living. 



Crania occurs in great numbers, adhering to stones, shells, branches of corals, &c, at 

 moderate depths ; but one species, C. anomala, is said to have been got at depths varying 

 from three to 808 fathoms. The genera and species of Clistenterata are found at depths 

 ranging from about half-tide mark to 2900 fathoms, Terebratula Wyvillei (Dav.) having 

 been obtained at the last-named depth in the Middle North Pacific ; it is an exceedingly 

 thin glassy shell. Another form was dredged by the same Expedition 300 miles east 

 of St. Paul's Rocks, Atlantic, at a depth of 1850 fathoms ; but the larger number of 

 species live at depths of from 5 to 300 or 400 fathoms, attached by their peduncles 

 to various marine objects, and very often to the outer surface of one another's shell; and 

 even young individuals to the peduncle of the parent shell, as I found to be very com- 

 monly the case with specimens of Terebratulina septentrionalis brought back by the " Chal- 

 lenger " Expedition, and in others given to me by Prof. Verrill. On a clustered specimen 

 of the last-named species, dredged at Lockport and measuring one inch in length by 

 three quarters of an inch in breadth, I counted thirty-seven young individuals attached, 

 and varying from the size of half a line in length up to five. Terebratulina septentrionalis, 

 as shown by Morse, varies much in shape during its growth. In quite young examples 

 the ribs are very few in number, but become gradually more numerous as the shell 

 increases in size. I have likewise clusters of Terebratella rubicunda from New Zealand 

 seas, as well as of Waldheimia flavescens, adhering to each other in a similar manner and 

 profusion. Some forms occur also in great numbers fixed by a shorter or longer peduncle 

 to coral-reefs ; and several minute species were found by Dr. Gwyn Jeffreys attached to 

 seaweeds. Kraussina rubra from the coast of Natal in South Africa was described by 

 Dr. Gray and myself as having been found attached in vast numbers to Ascidia and 

 stems of seaweeds. 



We may likewise note that a small species of Kraussina, {K. Davidsoni) was obtained 

 by M. Velain (during the Prench Expedition to make observations relative to the transit 

 of Venus) in the interior of the breached and sub-merged crater-basin of the Island of 

 St. Paul, attached in vast numbers to rocks at low-tide mark. I am also informed by 

 the same distinguished geologist that during the ordinary low tides they are scarcely 

 covered by water, are alternately covered and left bare at the ebb and flow of the tide, 

 and twice a month are left completely dry. They occur only in a vertical area of 

 a few yards in that region, and consequently at very shallow depths. 



